TAIPEI (Taiwan News) — The Taoyuan City Police raided three shops run by migrant workers from Southeast Asia on Thursday (Dec. 19) and discovered that the shops had been secretly used as illegal banks for the last six years.

The police said that it was the biggest illegal money transfer case in recent years and that four foreign workers were arrested for violating the Banking Act. According to Liberty Times, the suspects allegedly used food and apparel shops as fronts for their unlawful financing activities, receiving payments from compatriots in exchange for sending money back to their home countries.

Based on the accounting books found by the police, the suspects received commission fees as high as NT$2 million (US$66,300) for a single transfer. The police estimated that the four suspects have accumulated more than NT$7 billion (US$23 million) in profit, reported CNA.

The police added that clients of the shops were given "reward points" that could be exchanged for everyday accessories once they had used the remittance service several times. The police stressed that illegal banks could negatively impact Taiwan's financial system and warned foreigners that breaking the law is not worth the risk.