People for the Ethical Treatment of Animals filed a lawsuit against the Washington Metropolitan Area Transit Authority on Thursday, arguing the Washington, D.C., agency illegally barred the animal rights organization from advertising in the metro system.

The lawsuit objects to WMATA’s decision last year to bar three of PETA’s proposed advertisements from the D.C. metro because they violated the agency’s rule prohibiting “advertisements intended to influence members of the public regarding an issue on which there are varying opinions.” PETA argued that the transportation agency and General Manager Randy Clarke are violating the nonprofit group’s First Amendment rights by preventing them from placing their advertisements.