Macau authorities have broken up an illegal payment processing operation just as China launched a fresh crackdown on underground banking.

On Monday, Macau authorities arrested 17 individuals on suspicion of credit card fraud at five local stores selling jewelry and electronics. The scam allegedly utilized altered point-of-sale terminals that tricked financial outfit UnionPay into thinking the transactions were taking place in mainland China rather than in Macau.

Macau Judiciary Police said the scammers had conducted 4,549 transactions over the past 14 months that cheated UnionPay out of HKD 710k (US $91,600) in transaction fees. Police seized over HKD 13m in cash during the arrests.

The use of similarly altered mobile UnionPay devices made headlines last summer after Macau pawnshops and jewelry stores were caught processing bogus transactions intended to get around China’s currency exportation restrictions. Monday’s arrests followed Friday’s announcement of a new anti-money laundering cooperation deal between Macau and Beijing