An illegal immigration case led authorities in Macau to stumble upon a hotel’s scheme for its frequent Chinese gamblers, local media reported.

Local police arrested a Chinese man at the Outer Ferry Terminal last week, according to the Macau Business Daily. The man, surnamed Chen, had a blue card on him that identified him as a cleaning worker at a hotel in the city state. A blue card is a work permit issued to a non-resident who wants to work in Macau.

The man, however, told investigators that he was not a worker in the hotel, but he bought the work permit in 2014 from the hotel “to more easily facilitate his visits to the city for gambling.” Chen said he paid HK$50,000 (US$6,225) for the blue card, which he got through a friend in 2014.

Judicial Police refused to identify the hotel—but hinted that it was located “in the central area of the Peninsula”—because they are “still chasing” its agents and staff. Authorities believed the hotel “applied for blue cards for frequent Chinese gamblers to make money.”