Arguing that Greyhound is misinterpreting a federal law on immigration status checks that take place at a distance from international borders, the American Civil Liberties Union is urging the bus company to stop federal agents from boarding its buses and making arrests.

Ten ACLU affiliates, including New York State’s chapter, recently sent an open letter to Greyhound arguing that the company has a Fourth Amendment right to deny Customs and Border Protection agents access to its buses and that, to ensure the constitutional rights of its passengers, it must. Unless the agents have a judge-issued warrant, they shouldn’t be there, according to the ACLU.