The world's biggest carrier denied the allegations and said it would fight them in court.
"The struggle for inclusion at United Airlines is a long-standing issue that many have tried to address over a long period of time," Capt. Leon Miller, a plaintiff, said in a statement.
Most of those involved in the suit worked for pre-merger United. The complaint specifically addresses promotion issues dating to 2009.
Additionally, nearly half of the plaintiffs were part of a 2010 federal equal employment racial discrimination case against United, and are claiming that the carrier has punished them by withholding promotions and special assignments.
United said in a statement that it does not tolerate harassment or discrimination.
"We believe this lawsuit is without merit and will vigorously defend ourselves," the airline said.
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