OKLAHOMA CITY -- Authorities have shut down an illegal gambling operation in northwest Oklahoma City.

Sheriff's deputies and police found nearly 20 illegal phone card machines that worked as slot machines at Bingo City on Northwest 50th Street.

"Patrons would go up, put their money in and receive a phone card, and then they're allowed to gamble and get credit on the machine. And then they're able to cash out with a receipt and take that receipt to a cashier and get money for it," said Oklahoma County Sheriff's Spokesperson Mark Myers.

The 50 people inside were kicked out and nearly 20 workers were questioned.

The owner of the illegal machines could face felony charges