Lawyers for ICE provided false information to justify arresting and detaining thousands of people who had attended immigration courts, according to newly filed court documents.

Federal prosecutors said that lawyers for ICE acknowledged that an agency memo from May of last year gave no authorization for the arrests, court documents show, despite previously citing it to justify the arrests.

The revelation was included in filings by the office of Jay Clayton, a US federal attorney, in a lawsuit brought by the New York Civil Liberties Union and other civil rights groups, first reported on by the New York Daily News.

The lawsuit is challenging ICE’s practice of targeting people seeking to gain legal status in the US as they leave immigration courts. Agents have arrested thousands of people after they attended hearings, preventing them from further pursuing their cases.