Redflex Traffic Systems, the company that once installed and ran the city of Chicago's red-light cameras, became “unjustly enriched” after making approximately $100 million in “illgotten gains” through a contract provision letting the company receive up to 25 percent of $100 red-light tickets.

That's according to a class action lawsuit filed in federal court Thursday seeking "a return to the people who paid that money,” Thomas Cronin, the plaintiff's attorney, told the Chicago Sun-Times. “That extra charge was uncalled for because it was negotiated by bribery.”

The suit, which still needs a federal judge to OK the class action status, was brought by Credit Suisse banker and Chicago resident Matthew Falkner. The suit aims to give back the funds to those who were issued red-light tickets under Redflex.

Federal prosecutors say John Bills, a now-retired city official who was previously responsible for managing Chicago's red-light camera system, allegedly steered $124 million in city contracts to Phoenix-based Redflex in exchange for cash and other personal benefits, including a $177,000 Arizona condominium. Bills was arrested in May on a federal bribery charge in connection with the scandal.

The city fired Redflex as its vendor in 2013.