IRS-ICE data-sharing agreement sidesteps Congress’s authority, amicus brief argues

The IRS’s data-sharing agreement with Immigration and Customs Enforcement “improperly challenges” the authority Congress has over the protection of taxpayer data, a group of 115 Senate and House lawmakers argued in an amicus brief filed Thursday.

The Democratic lawmakers’ filing in the U.S. Court of Appeals for the D.C. Circuit was made in support of the Center for Taxpayer Rights and a handful of labor groups in their lawsuit against the IRS over the memorandum of understanding it signed last year with ICE.

The new brief, led by Sens. Catherine Cortez Masto of Nevada and Alex Padilla of California, and Reps. Adriano Espaillat of New York, Linda T. Sánchez of California and Jimmy Gomez of California, makes the case that Congress’s legislative powers are undermined by the MOU. 

“We are alarmed that this Administration is seeking to rewrite section 6103 or to disregard its requirements,” the brief states, referring to federal tax code that guarantees confidentiality of taxpayer information. 

The decision to share that data with the Department of Homeland Security component represents a violation of “the express terms of the statute and its history,” the brief continued. “Congress rejected several proposals to use return information for immigration enforcement purposes to section 6103. Instead, Congress and the IRS, acting on delegated authority, promoted voluntary compliance by immigrant taxpayers by protecting their information.”

The brief, which was signed by another nine senators and 101 representatives, makes the case that the “high rate of voluntary compliance involving millions of taxpayers” has been damaged by the MOU. The decision to wield taxpayer data as an immigration enforcement tool will likely deprive the federal government of much-needed tax revenue, the brief argues.

“Congress has consistently prioritized revenue collection over the competing goal of using taxpayer information for immigration enforcement not only by safeguarding the confidentiality of return information but also by encouraging voluntary compliance on the part of all taxpayers, including those who lack authorization to work in the United States,” the lawmakers wrote. “Immigration status has no relevance in our tax system, which instead applies a substantial presence test and imposes tax on ‘resident aliens.’”

The amicus brief also takes the IRS to task over what it says are violations of the Administrative Procedure Act, which governs agency rulemaking. In a different lawsuit over the data-sharing agreement, a federal judge in Massachusetts last month blocked ICE from using taxpayer information, citing improper agency rulemaking and the “high potential for misidentification.”

“Congress has a direct and vested interest in ensuring that the IRS complies with both substantive law and the APA’s procedural safeguards, particularly given the consequences of the IRS’s arbitrary and capricious decision for our country’s finances, tax system, and taxpayer privacy,” the new amicus brief states. “To determine IRS’s compliance with these standards, this Court must base its assessment on the grounds upon which the IRS actually acted, not on post hoc rationalizations developed for litigation.”

The lawmakers’ brief was filed as the D.C. appeals court considers a challenge to Judge Colleen Kollar-Kotelly’s November 2025 ruling to bar the IRS from sharing taxpayer addresses with ICE. Documents released in the lead-up to that ruling revealed an ICE request for nearly 1.3 million taxpayer records, with more than 47,000 matches coming from that ask.

Last month, the IRS’s chief risk and control officer acknowledged in a court filing that the tax agency improperly shared much of that data, violating the MOU’s provisions and possibly federal privacy law. Judge Kollar-Kotelly wrote in a subsequent court filing that that admission essentially meant that the IRS broke federal law “approximately 42,695 times.”