TULSA, Okla. — Two national civil rights groups have joined a federal lawsuit accusing dozens of Oklahoma sheriffs, judges and court clerks of operating a debt-collection scheme that preys on poor people by sending them to jail if they can’t pay court costs.

Georgetown University’s Institute for Constitutional Advocacy and Protection and Civil Rights Corps joined an amended complaint filed late Thursday in Tulsa.

The initial lawsuit filed in November accuses the Oklahoma Sheriffs’ Association, debt collection firm Aberdeen Enterprizes II and others of violating the Constitution by conspiring to collect court costs and unpaid fines without regard to a defendant’s ability to pay.

The suit seeks to halt further arrests of indigent people until the case can go before a judge.

Messages to the sheriffs’ association and Aberdeen weren’t immediately returned Friday.