The IRS erroneously shared the taxpayer information of thousands of people with the Department of Homeland Security, as part of the agencies' controversial agreement to share information on immigrants for the purpose of identifying and deporting people illegally in the U.S, according to a new court filing.The revelation stems from a data-sharing agreement signed last April by Treasury Secretary Scott Bessent and Homeland Security Secretary Kristi Noem, which allows U.S. Immigration and Customs Enforcement to submit names and addresses of immigrants inside the U.S. illegally to the IRS for cross-verification against tax records.A declaration filed Wednesday by IRS Chief Risk and Control Officer Dottie Romo stated that the IRS was only able to verify roughly 47,000 of the 1.28 million names ICE requested.For less than 5% of those individuals, the IRS gave ICE additional address information, potentially violating privacy rules created to protect taxpayer data.Romo added that Treasury notified DHS in January of the error and requested DHS' assistance in "promptly taking steps to remediate the matter consistent with federal law," which includes "appropriate disposal of any data provided to ICE by IRS based on incomplete or insufficient address information."The IRS-DHS agreement set off litigation between advocacy groups and the federal government last year. Public Citizen filed a lawsuit against the Treasury secretary, the Homeland Security secretary and their respective agencies on behalf of several immigrant rights groups shortly after the agreement was signed.Most recently, a Massachusetts federal court ordered the IRS to stop sharing residential addresses with ICE. And last November, a federal court blocked the IRS from sharing information with DHS, saying the IRS illegally disseminated the tax data of some migrants last summer.The news of the erroneous disclosure was initially reported by The Washington Post. A spokesperson from the IRS did not respond to an Associated Press request for comment.Advocates fear that the potential unlawful release of taxpayer records could be used to maliciously target Americans, violate their privacy and create other ramifications.Lisa Gilbert, co-president of Public Citizen said that "this breach of confidential information was part of the reason we filed our lawsuit in the first place. Sharing this private taxpayer data creates chaos and, as we've seen this past year, if federal agents use this private information to track down individuals, it can endanger lives."Tom Bowman, policy counsel for the Center for Democracy & Technology said that "the improper sharing of taxpayer data is unsafe, unlawful, and subject to serious criminal penalties.""Once taxpayer data is opened to immigration enforcement, mistakes are inevitable and the consequences fall on innocent people," Bowman said. "The disclosure of thousands of confidential records unfortunately shows precisely why strict legal firewalls exist and have — until now — been treated as an important guardrail."