BOISE, Idaho (AP) — Northern Idaho police have launched a criminal investigation probing the legality of slot-like machines known as instant horse racing terminals, which are slowly gaining popularity across the state.

Post Falls Police Chief Scot Haug says detectives are responding to a complaint claiming that the roughly 10 terminals installed at Greyhound Park and Event Center are illegal slot machines and not state-approved pari-mutuel betting terminals. Haug added that he expects to complete the investigation in a month. Instant racing was legalized in in Idaho in 2013 after horse industry representatives argued they needed them to save their dying trade.

However, the legality of the machines is currently being challenged in other states. Earlier this year, four Idaho tribes have demanded state officials to cease all use of the machines.