The American Civil Liberties Union lost a case about offensive speech and workers’ rights — over its own workplace.

A judge ruled on Wednesday that the A.C.L.U. had illegally fired an employee, Kate Oh, from her job as senior policy counsel. The group had accused her of using language that was racist and that singled out people of color in the office.

Michael A. Rosas, an administrative law judge, said that the A.C.L.U.’s accusation that she had targeted people of color “is not borne out by the facts.” He noted that her complaints were not about colleagues but superiors within the organization, and that she had also complained about white managers.

Ms. Oh never uttered a racial slur or invoked race, court filings showed. She said that she considered herself a whistle-blower and advocate for other women in the office, drawing attention to an environment she said was rife with sexism and fear. Her frequent, sometimes intemperate, complaints irritated her bosses, she argued, so they retaliated by firing her.

The case placed one of the nation’s leading defenders of workers’ rights under scrutiny for violating the very workplace protections it typically seeks to enforce.

The judge ordered the A.C.L.U. to reinstate Ms. Oh, who was fired in May 2022, and to give her back pay.