Washington DC - A federal judge has blocked the Internal Revenue Service from providing US Immigration and Customs Enforcement with taxpayer information to assist in their mass roundups of immigrants.

In a 94-page ruling handed down on Friday, US District Judge Colleen Kollar-Kotelly ruled in favor of the Center for Taxpayer Rights (CTR) in a lawsuit it had brought against the IRS over its information sharing with ICE.

The CTR had argued that the IRS' plans to share information, including the addresses of undocumented migrants, was "unlawful" because it endangered confidentiality and violated privacy and data sharing laws.

Kollar-Kotelly said that there was a "substantial likelihood" that the IRS-ICE data sharing agreement violated the service's own confidentiality rules.

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She argued that the IRS had "failed to consider the reliance interests that were engendered by its prior policy of strict confidentiality, and failed to provide a reasoned explanation for the new Policy."

"The IRS's implementation of the Address-Sharing Policy was arbitrary and capricious because the IRS failed to acknowledge and explain its departure from its prior policy of strict confidentiality," Kollar-Kotelly wrote.

Friday's ruling stated that the IRS had also "failed to consider the reliance interests that were engendered by its prior policy of strict confidentiality, and failed to provide a reasoned explanation for implementing the new Address-Sharing Policy."

The IRS agreed to share tax information with ICE and by extension the Department of Homeland Security in April, including taxpayer's addresses, income, and broader details about the families of undocumented migrants

Then-acting IRS Commissioner Melanie Krause announced her resignation days later amid rumors that she had opposed the agency's facilitation of President Donald Trump's anti-immigrant policies.

Krause's refusal to sign the data-sharing agreement reportedly led Treasury Secretary Scott Bessent to override her authority and sign the document himself.