Commentary

How the Federal Government Can Prevent Undue Burdens to Interstate Commerce

by Andrew Wilford, Tyler Martinez September 22, 2025

On behalf of National Taxpayers Union Foundation (“NTUF”), we write with comments on some of the most significant burdens faced by individuals and businesses attempting to engage in economic activity across state lines.

For nearly five decades, NTUF has striven to give policymakers the tools to make informed, pro-taxpayer policy choices. The question here is of particular interest to our organization, as our Interstate Commerce Initiative was founded out of concern for the growing problem of states taxing and regulating Americans outside their borders in an increasingly mobile and interconnected economy.

We would like to bring to your attention just some of the most pressing interstate commerce issues that are weighing down our economy. In particular, we have focused on issues where actions by certain states are not only harming taxpayers in other states, but also having a deleterious effect on the broader national economy.

In all of these cases, state actions are harming nonresidents who have little recourse with their elected representatives at the state level — the harm is coming from states where they do not reside and lack voting power of any sort. Their only possible recourse is the federal government, which has a vital interest in ensuring that states do not unduly burden interstate commerce.

Reining in State Income Tax Assessments Against Out-of-State Businesses

Background

Back in 1958, the Supreme Court issued its opinion in Northwestern Cement Co. v. Minnesota, 358 U.S. 450 (1959, which greenlit a Minnesota income tax assessment against an Iowa-based business with no presence in Minnesota aside from a three-employee sales office sending orders back to Iowa for fulfillment. Alarmed by the potential consequences of states imposing income tax obligations on remote businesses based on very limited connections, Congress quickly acted to pass the Interstate Income Act of 1959, better known as Public Law 86-272.¹

This law simply codifies that states cannot impose business income tax obligations on out-of-state businesses with no physical presence in-state aside from soliciting and fulfilling sales of tangible personal property. P.L. 86-272 was meant as a stopgap while a special committee prepared a report on a more comprehensive solution. But that more permanent solution never came, leaving this statute as the last Congressional action on the books for protecting the nation’s economy from duplicative state business tax burdens.

The volumes of the Willis Committee report, released between 1964 and 1965, recommended a uniform tax base that covered nearly all retail sales,² a uniform two-factor business tax apportionment standard including only payroll and property, and authority given to the Treasury Department to establish model business income tax rules and a model state tax return. The nation soon became preoccupied with other matters during 1964 and 1965, leaving the Willis Commission’s more comprehensive solutions on the drawing room floor. But P.L. 86-272 remained, much to some states’ chagrin.

The Problem

Rather than easing the burdens that led to P.L. 86-272’s enactment, states have focused on chipping away at the protections offered by P.L. 86-272 and dismissing any need for greater uniformity. A recent effort by the Multistate Tax Commission (MTC) and spearheaded by California, New York, and New Jersey represents a particularly brazen attempt.

California and its ilk ran with ideas generated in 2021 by the MTC. In the summer of 2021, the MTC released a Statement of Information on P.L. 86-272 that claimed that selling through virtually any modern website should exceed the law’s protections.³ Much of the MTC’s guidance relies upon the dubious position that any form of digitization automatically forfeits protection under P.L. 86-272. Fundamentally, the MTC construes “solicitation” in the narrowest sense possible, claiming that even the most basic actions necessary to facilitate solicitation are outside the scope of P.L. 86-272. Following the MTC’s logic will be devastating to the United States’s leadership in new technology as every online platform begins to worry about multiple levels of state and local taxation and regulation of activity that is, fundamentally, in interstate and international commerce.

For instance, the MTC guidance lists the following activities as forfeiting P.L. 86-272 protection:

Offering post-sale customer support through email or chat initiated through a button on the seller’s website (the MTC considers a static FAQ page to still be protected)
Allowing website visitors to submit applications for open jobs through a portal on the website (a physically mailed-in job application would still be allowed)
The use of digital “cookies” to “adjust production schedules and inventory amounts, develop new products, or identify new items to offer for sale.”⁴

The full list of protection-forfeiting activities under the MTC guidance is far longer, comprising a gauntlet of landmines a modern business would struggle to navigate.

Since the release of the MTC’s guidance, three states have acted to implement language closely mirroring the MTC’s, all through regulatory action and not by legislation. California, acting first in early 2022, tried to bypass even the regulatory notice-and-comment period with a simple Technical Advice Memorandum, though this effort was struck down following a court challenge.⁵ New York (December 2023)⁶ and New Jersey (June 2025)⁷ have since published formal regulations adopting the MTC’s interpretation of P.L. 86-272.

Other states have also taken aim at P.L. 86-272’s protections without formally adopting the MTC’s position. Revenue department representatives for Alaska, Kansas, Utah, and Wisconsin all indicated that they would follow the MTC’s interpretation of P.L. 86-272, while Michigan and North Carolina indicated that they would follow it in part.

Other states have attempted to circumvent P.L. 86-272 in different ways. Most egregiously, Hawaii has taken the position that any business with no physical presence in the state but that exceeds $100,000 in sales or 200 transactions forfeits the protection of P.L. 86-272, a position with no basis in the underlying law that even the MTC explicitly rejects.⁸

The new technology economy — so vital to US leadership in the world — is now subject to balkanized regulations at the whims of regulators in Hawaii, California, New York, and other states.

In another case, Minnesota claimed that Uline Co., a Wisconsin-based business, exceeded P.L. 86-272’s protections because its sales representatives collected “market research notes” during the course of their sales visits in Minnesota and sent them back to Uline’s Wisconsin offices. The idea that sales representatives could possibly not glean information about the market when interacting with their customers, or that that would be outside the scope of solicitation, stretches credulity. Yet in a sign of just how far P.L. 86-272’s protections have been eroded in courtrooms over the years, Minnesota’s Supreme Court sided with Minnesota on the issue.⁹

Should states like New York and California succeed in these sorts of legal acrobatics, small businesses will be left facing immense paperwork burdens. It is true that most of the largest businesses engaged in interstate commerce already engage in activities outside the scope of P.L. 86-272 in most states, and have the capacity to handle compliance across the nation where they do not. But the opposite is the case for small businesses, which must increasingly use their limited resources just to understand each state’s varying tax compliance regulations. Congress wanted the exact opposite: that is the very purpose of P.L. 86-272. This Administration can enforce existing law to protect America’s economy.

Solutions

The Department of Justice should take legal action against states that are deliberately violating federal law. Not only would correcting violations of P.L. 86-272 by Hawaii, New York, or New Jersey be well within the federal government’s jurisdiction, it would carry greater weight in courts that are often inclined to view disputes over tax matters as mere efforts to sidestep tax obligations when brought by taxpayers themselves. In other words, the weight of the federal government siding with small businesses will turn the tide against the petty bureaucrats.

The Department of Justice should issue a rule clarifying and strengthening the definition of “solicitation of orders” to reinforce that activities that facilitate solicitation are also protected. H.R. 8021, the Interstate Commerce Simplification Act of 2024, proposes to do this. The operative portion of this legislation would have added that “solicitation of orders” comprises “any business activity that facilitates the solicitation of orders even if that activity may also serve some independently valuable business function apart from solicitation.”¹⁰ Given that much of the danger lies in states taking too narrow a view of what is "solicitation" for interstate commerce, a federal regulation making this definition clear is in line with the clear intent of the original legislation and would prevent states from misconstruing P.L. 86-272 to avoid complying with the law.

Easing the Crushing Sales Tax Compliance Burden on Small Businesses

Background

Prior to 2018, states could only claim that a retailer had sales tax nexus if a retailer had some form of physical presence located in that state — meaning a warehouse, a retail outlet, or employees. For most small remote retailers, this meant that they were only required to collect and remit sales tax to their home state. Consumers who did not pay sales tax on a transaction were obligated to remit use tax to their home state instead, though in practice this obligation often went unfulfilled (largely out of ignorance on the part of consumers).

In 2018, the South Dakota v. Wayfair decision upended this practice.¹¹ In this decision, the Supreme Court approved a South Dakota law requiring out-of-state businesses that exceeded 200 transactions or $100,000 in sales to South Dakota consumers to collect and remit South Dakota sales tax. Physical presence was no longer necessary for states to require a retailer to collect and remit sales tax on their behalf. What states heard is that they could tax internet sales, some forgetting about important guardrails in the South Dakota law that the Supreme Court approved.

The South Dakota law at issue in the Wayfair case had three key elements that led the Supreme Court to deem that it did not unduly burden interstate commerce:

A safe harbor for small sellers
A ban against retroactive enforcement
Streamlined Sales and Use Tax Agreement (SSUTA) membership, which entails:
- State-level administration of sales taxes
- Uniform definitions of products and services
- Simplified tax rate structures
- Access to tax compliance software provided to retailers by the state

This new form of nexus, known as “economic nexus,” quickly spread to all 45 states with a sales tax, as well as D.C. and Alaska (which has local sales tax jurisdictions). However, many considered the above “Wayfair checklist” to be more suggested than mandatory. Most states simply copied South Dakota’s 200 transaction/$100,000 in sales thresholds, even though South Dakota is one of the smallest states in the nation. Kansas, in fact, went without any safe harbor at all from 2019 to 2021.¹² States like Massachusetts have continued to attempt to enforce pre-Wayfair laws.¹³ And no new states have joined the SSUTA since the Wayfair decision, leaving the agreement’s membership at just 24 states — while none of the six largest states by GDP are in the SSUTA.

The Problem

For small sellers, Wayfair meant that nearly overnight, they went from having to comply with just a single sales tax regime to having to comply with as many as 46 — even before factoring in local taxing jurisdictions. Each new state can mean a whole new set of classifications, exemptions, and rates. Small businesses also face many more potential sources of audits, which, even when not turning up any errors, can be extremely costly.¹⁴

To illustrate the degree of complexity small sellers are facing, even the safe harbors meant to protect them are quite complicated across 46 states and D.C.¹⁵ Some states base their safe harbor thresholds on retail sales, while others use taxable sales or even gross sales. Some states exclude marketplace sales from individual sellers’ safe harbor thresholds, while some do not. Some states measure progress towards their safe harbor thresholds in calendar years, some use the previous 12-month period, and Connecticut uses 12-month periods ending at the end of September.

So if keeping track of the rules governing whether or not a business has to even begin complying with a state’s sales tax obligations is already difficult, one can imagine the impossible position small businesses face when it comes to collecting and remitting sales tax on behalf of 46 states and D.C. Tax compliance software, promised as a panacea to these woes, has often proven insufficient and costly.¹⁶

And while most people think of Amazon or Walmart when they think of online retail, these businesses were largely unaffected by the Wayfair decision. Amazon had voluntary sales tax collection agreements (as well as physical presence in the form of warehouses) with every state with a sales tax prior to Wayfair, while Walmart had nexus through physical retail outlets.

More to the point, however, these businesses had decades to build up the state and local tax expertise necessary to comply with taxing jurisdictions around the country, and had the resources to maintain them. Small businesses around the country have neither of those advantages.

Consequently, small business owners are struggling to keep up. Just half of all small business owners, and only 60 percent of larger businesses, self-reported being “completely compliant” with their economic nexus obligations¹⁷ — numbers which do not even account for overconfident respondents or past noncompliance that has not been rectified. That means that at least around half of online retail businesses, and possibly much, much more, are operating with a sword of Damocles hanging over them — should states come to collect that revenue that businesses never collected from consumers in the first place, those businesses will struggle to survive.

And audits are already beginning to spike as state budgets get tighter. TaxValet, a sales tax compliance company, found that audits more than quadrupled among their customers between 2021 and 2023.¹⁸ This state of affairs risks crushing small businesses and imposing a barrier to entry to the e-commerce industry that is so enormous that new innovation is stifled.

It is also worth noting that the present state of affairs is not advantageous to states, either. Substantial numbers of businesses are not complying with their obligations, most of which are either unaware of or unable to fulfill these burdens. Most businesses, particularly small businesses, would much prefer to operate within the boundaries of the law than face catastrophe and criminal prosecution. Reducing compliance burdens is the key to boosting compliance and, consequently, state revenues.

Solutions

The Department of Justice should issue an advisory opinion stating that it is the position of the United States government that states must meet the minimum standards outlined by the Supreme Court in South Dakota v. Wayfair in order for their economic nexus-based sales tax obligations on remote sellers to be constitutional. As detailed above, states have by and large treated Wayfair as a blank check to impose economic nexus obligations on out-of-state businesses however they please. An advisory position issued by the United States government would help courts to recognize the gravity of the compliance burdens that small businesses are facing and encourage courts to hew more closely to the Wayfair standard.

In particular, states that are not members of the Streamlined Sales and Use Tax Agreement should be held to higher standards of closeness to the South Dakota law at issue in Wayfair. For non-SSUTA states, remote sellers should be subject to no more than one tax rate per state, and no more than one point of contact for compliance and audits. States should also be required to maintain safe harbors with thresholds no lower than that of South Dakota in the Wayfair case.

Senator Maggie Hassan’s discussion draft on potential guardrails that Congress should consider requiring states to abide by in this area would serve as an excellent framework.¹⁹ For the purposes of the Department’s request for comments, enforcing the contours of Supreme Court decisions on interstate commerce are well within Federal jurisdiction.

The federal government should investigate ways that the federal government can limit the compliance burden of multistate tax filing for small remote businesses. This could include developing an optional centralized tax compliance system that would be capable of collecting and remitting revenue on behalf of all states, or coordinating non-SSUTA states to piggyback on the SSUTA program of certifying compliance software providers that are able to collect and remit on behalf of sellers, with sellers held harmless for errors made on the part of these certified service providers. On the state level, Texas has a central clearinghouse option that small businesses can use.²⁰ The Federal government can offer a similar one-stop solution.

Additionally, the federal government could offer other ways to streamline the filing process by creating universal forms such as exemption certificates, and requiring states to recognize and accept them. When the information that states need to verify that a transaction is indeed tax exempt is largely the same across 46 states, there is little reason to have more than one version of a form.

Updating Irrational State Income Tax Rules in the Modern Era

While many Americans have found convenience in the increasingly digital work arrangements that have persisted in some form since the pandemic, they have also found that increased mobility carries with it new state tax burdens.

Remote work, while no longer as prevalent as it was during the pandemic, has remained a common practice — just 19 percent of employees in occupations capable of working remotely now work entirely in the office.²¹ Technology improvements and increased acceptance of these types of work arrangements have also enabled Americans to travel and work, whether as “digital nomads” or just by doing their normal 9 to 5s remotely for a few days while they visit family.

The Problem

Many of these new working arrangements entail tax complications, however. Most Americans are surprised to find out that in many states they are expected to file separate state income tax returns based on a single day spent working in a state for a conference, retreat, sales visit, and so on. Answer a work email while on vacation in Colorado? You should be filing a Colorado income tax form for that day’s work. Employers are often on the hook as well, required to withhold income tax on behalf of employees who spend short periods of time working in a state.²²

In such cases, it is not the actual tax liability that is the problem. For a short period of work in a state for the average taxpayer, the value of the time spent and the additional cost to add another state to tax software will often exceed the actual tax dollars remitted. That means that not only are individual taxpayers and their employers subjected to onerous compliance burdens, state revenue departments must expend valuable resources and effort to process these small-dollar returns.

Not only does this represent a substantial deadweight loss on the aggregate, it also can dissuade individuals and businesses from earning income across state lines on a short-term basis. It is one thing for states to drive businesses away by overtaxing them, but for the country to miss out on productive economic opportunities due to paperwork is a pointless loss.

While much of this tax hassle comes from inertia on states’ part, in some cases states are taking deliberate advantage of the complications of multistate tax compliance to maximize the revenue they take from nonresidents. One of the worst examples of this is the “convenience of the employer” rule first introduced by New York, though Alabama, Connecticut, Delaware, Nebraska, New Jersey, Oregon, and Pennsylvania also apply the rule in some form. In New York’s case, this rule requires in-state New Yorkers who move to another state to work remotely for the same New York-based employer to continue paying New York income taxes.

Not only is this rule and its copycat versions in other states unfair and illogical, it can also subject affected taxpayers to double taxation. Preventing more than one state from taxing the same income is something the federal government has a strong interest in.

An opportunity to end this practice was allowed to come and go in New Hampshire v. Massachusetts.²³ Massachusetts had imposed a version of the convenience of the employer rule during the pandemic, and New Hampshire took legal action for the unwarranted effort by the state to tax New Hampshirites living and working in New Hampshire. The Supreme Court declined to hear the case, however, likely because Massachusetts allowed application of the rule to expire in the meantime.

States have also taken advantage of the complications in income tax aggregation. A recent example was the court case Zilka v. Philadelphia.²⁴ In this case, Diane Zilka, a Philadelphia resident, commuted to Wilmington, Delaware for work. Zilka owed income tax at different rates for each state and locality — 3.922 percent to Philadelphia, 3.07 percent to Pennsylvania, 1.25 percent to Wilmington, and 5 percent to Delaware.

While in the aggregate, the state-local tax rates were fairly similar (6.992 percent for Pennsylvania and 6.25 percent for Delaware), Philadelphia took advantage of the fact that Delaware’s tax burden skewed towards the state level rather than the local level to only offer to credit Zilka’s 1.25 percent Wilmington tax against its own 3.922 percent tax rate. By refusing to factor in state-level taxes, Philadelphia was making a distinction without a difference — local taxing jurisdictions represent mere devolutions of states’ own taxing powers.²⁵

Unfortunately, the Pennsylvania Supreme Court sided with Philadelphia, and the United States Supreme Court declined to take up the case on appeal. This means that states face no restriction on gaming the system of credits to prevent multiple taxation if they structure their tax codes to encourage high local-level taxes. There is little reason why taxpayers should face multiple taxation just because of imbalances between the ratio of state income taxes that come from states compared to localities.

Solutions

The Department of Commerce should advise states to adopt 30-day safe harbors for filing and withholding. The rules currently vary widely by state, but the best states, such as Indiana, Illinois, and Louisiana, have safe harbors that exempt nonresidents from any obligation to file an individual income tax return until they spend 30 days working and earning income in the state. A federal version of this idea has been introduced as bipartisan legislation many times in the past, including most recently by Sens. Thune (R-SD) and Cortez-Masto (D-NV),²⁶ and Department of Commerce endorsement would ease the path to reform at both the state and federal levels.

The Department of Commerce should shepherd the creation of an interstate income tax reciprocity compact. Many states have already entered into bilateral income tax reciprocity agreements in which both states agree not to tax residents of each other’s states and assign all income earned in either state to the individual’s state of residence. This concept should be expanded into a multilateral agreement under which all member states assign income earned in any other member state to the individual’s state of residence.

The Department of Justice should correct misguided Biden administration filings in New Hampshire v. Massachusetts and Zilka v. Philadelphia. The Department of Justice weighed in unhelpfully in both cases under the Biden administration. In New Hampshire v. Massachusetts, the Biden administration argued that the issues in the case were pandemic-specific and therefore transitory.²⁷ That was a mistake — as previously stated, eight states continue to enforce convenience of the employer rules. Even if temporary, the Supreme Court should have declared Massachusetts’s actions unconstitutional, and the Trump administration Department of Justice should make it clear to judges that they should do the same if faced with a challenge to any other so-called “convenience of the employer” rules.

In Zilka, the Biden administration likewise encouraged the Supreme Court not to take up the case, dismissing fears of states gaming the system by restructuring their tax codes to minimize the amount they need to credit against taxes in other states because “no State has apparently done so.”²⁸ The bizarre argument that no state has taken advantage of the outcome of Zilka before Zilka had even reached the Supreme Court’s docket does not befit the United States government, and should be disavowed. The Department of Justice should issue an advisory opinion making it clear that Comptroller v. Wynne is still good law and is sufficient to rule such state-local aggregation games unconstitutional.

Digital Services Taxes

The Problem

In recent years, other nations have sought to take advantage of the strength of the United States’ tech sector by assessing special taxes on digital services. The United States government, having found that digital services taxes (DSTs) disproportionately harm American businesses,²⁹ has rightly treated these assessments as anticompetitive barriers to trade where they have arisen. This has remained a key point in trade negotiations, with the United States seeking to have foreign nations agree not to impose special taxes on digital services.³⁰

Yet a similar dynamic has played out simultaneously at the state level, which serve to undermine our international negotiation efforts. Maryland became the first state to pass a digital advertising tax in February of 2021, with the new assessment going into effect in 2022. The tax was structured in such a way as to ensure that it would fall upon out-of-state businesses, with businesses with less than $100 million in digital advertising revenue worldwide exempted.³¹ Much like DSTs at the international level, Maryland’s tax unsubtly functions like a tariff on digital advertising services. Maryland’s tax remains the only one at present at the state level, but other states are considering emulating them.

Maryland’s tax quickly faced an array of legal challenges that, according to University of Maryland professor Samuel Handwerger, “read like a constitutional law textbook.”³² Constitutional provisions and laws that Maryland’s law have been challenged under include:

The First Amendment: for targeting a primary source of revenue for news media for special tax assessment and for prohibiting businesses from informing their customers that prices may increase as a result of the tax. The Fourth Circuit Court of Appeals recently struck down the part of the law that prevented businesses from explaining price increases.³
The Commerce Clause: for exporting tax burdens outside Maryland’s borders in a clear attempt to target out-of-state businesses.
The Due Process Clause: for attempting to tax and regulate conduct undertaken almost entirely by out-of-state businesses.
The Internet Tax Freedom Act: for levying a discriminatory tax against digital services that does not apply to traditional forms of advertising.

The Solution

The Department of Justice should take legal action against Maryland for violating the Foreign Commerce Clause of the Constitution. Along with the above litany of legal pitfalls, Maryland’s actions also manage to violate a provision of the Constitution that is usually too straightforward to require litigation. The Foreign Commerce Clause of the Constitution assigns responsibility for regulating foreign trade to the federal government. The Supreme Court has ruled that state actions that undermine foreign trade negotiations undertaken by the federal government represent violations of this provision as well.³⁴

A state like Maryland doing to businesses in other states precisely what the federal government is in the process of trying to prevent other nations from doing to American businesses clearly undermines the federal government’s ability to conduct these trade negotiations effectively. While a multitude of legal actions by private businesses have already been taken against Maryland, legal action by the federal government would elevate these arguments past the level of a mere tax dispute. The Constitution created a stronger federal government precisely to avoid these sorts of problems.

Even setting aside all of the other likely fatal legal and constitutional violations that the Maryland law entails, federal action in this case is warranted. It is likely that Maryland’s willingness to act in such a cavalier fashion has already harmed the federal government’s position in trade negotiations — states should be made to think twice before doing so again in the future.

Conclusion

We thank you for your attention to and consideration of these recommendations. While this list of interstate commerce challenges is not comprehensive, we have aimed to identify those that are causing the greatest injury to the broader national economy, or that carry the greatest risk of doing so in the near future.

We stand ready to advise and assist should you have any further questions.

Sincerely,

Andrew Wilford, Director of the Interstate Commerce Initiative

Tyler Martinez, Senior Attorney

¹ In policy circles, the law is referred to by its public law number, but it is codified at 15 U.S.C. § 381.

² Under the recommendations in the report, states would handle sales tax exemptions in the form of refunds.

³ See the full MTC Statement of Information at https://www.mtc.gov/wp-content/uploads/2023/04/025-MTC-Statement-on-PL-86-272.pdf.

⁴ Other uses of digital cookies are theoretically possible to use within the bounds of P.L. 86-272, though proving that the use of cookies in no way contributed to adjusting production schedules or inventory would be nearly impossible.

⁵ See a copy of the original TAM 2022-01, which has since been removed from the FTB’s website, here: https://www.law360.com/tax-authority/articles/1464971/attachments/0.

⁶ See https://www.tax.ny.gov/rulemaker/adoptions/corp/2023.htm#om121123. .

⁷ See https://www.law360.com/tax-authority/articles/2353735/attachments/0.

⁸ See https://files.hawaii.gov/tax/legal/tir/tir20-05.pdf. For MTC position on applicability of P.L. 86-272 even in cases where economic thresholds are exceeded, see https://www.mtc.gov/wp-content/uploads/2023/04/025-MTC-Statement-on-PL-86-272.pdf, pg. 17.

⁹ See https://law.justia.com/cases/minnesota/supreme-court/2024/a23-1561.html.

¹⁰ See https://www.congress.gov/bill/118th-congress/house-bill/8021/text.

¹¹ See https://www.supremecourt.gov/opinions/17pdf/17-494_j4el.pdf.

¹² See https://www.ntu.org/foundation/detail/kansas-must-act-to-protect-small-sellers-from-remote-sales-tax-law.

¹³ See https://www.ntu.org/foundation/detail/ntuf-advises-the-massachusetts-supreme-judicial-court-to-rule-against-retroactive-sales-tax.

¹⁴ See https://www.ntu.org/foundation/detail/reforms-congress-must-consider-4-years-after-wayfair-ruling.

¹⁵ See https://www.salestaxinstitute.com/resources/economic-nexus-state-guide.

¹⁶ See https://www.ntu.org/library/doclib/2024/07/2024tns14-7.pdf.