WASHINGTON-The Trump administration violated federal law when it shared confidential taxpayer information with immigration authorities, an appeals court ruled Tuesday.

The Internal Revenue Service improperly allowed data transfers based on partial addresses and failed to satisfy requirements that tightly tie legal information sharing to criminal investigations, according to the U.S. Circuit Court of Appeals for the District of Columbia. The court left in place a lower-court ruling that has blocked further data sharing.

"The IRS is now on notice twice over regarding the legal inadequacies of its summer 2025 disclosures," Judge Cornelia Pillard wrote for a unanimous three-judge panel in a case brought by a taxpayer-rights group. "The government and its personnel face steep civil and criminal consequences for willful disclosure of information."

The tax code creates broad protections for taxpayers' information, allowing limited exceptions when IRS employees can disclose data outside the agency. Protected records include information provided by people who are in the country illegally. For many years, the government had encouraged those people to file returns and be compliant with the tax law, assuring them that they wouldn't share information with immigration authorities.

Trump administration officials, however, were eager to use the government's trove of tax data for immigration enforcement. They ran into resistance in the IRS when they tried to get tax records early in the administration, and broad requests were rejected.

But they eventually zeroed in on one exception in the law. The law requires tax authorities to provide information to federal agencies conducting criminal inquiries, including investigations of people who have failed to follow final orders of removal from the U.S.

The IRS and Immigration and Customs Enforcement set up a procedure that let immigration officials submit lists to tax authorities to check against their records. ICE sent more than one million names to the IRS, which turned over more than 47,000 records in response.

But the procedure and its implementation had flaws, ruled the judges. The law requires requests to include a name and address, but in some cases, the IRS turned over taxpayer information in response to partial or incomplete addresses.

The IRS-ICE agreement had another flaw, the court ruled. The IRS provided a last known address for taxpayers, not a date. That information isn't necessarily about the period after a removal order that would pertain to a criminal investigation, and thus the approach "systematically will cause IRS to continue to ignore that statutory requirement," the court ruled.

An IRS spokesman didn't immediately respond to a request for comment.