The Department of Business Development (DBD) uncovered suspected legal violations during a joint inspection of businesses in Bangkok's Huai Khwang district.
The operation followed media reports that a Chinese restaurant had refused to accept payment in Thai baht and amid growing concerns over the use of Thai nominees.
The DBD said it conducted the inspection with officials from the Immigration Bureau and the Department of Employment last week.
Their targets included restaurants, supermarkets and property agencies along Pracha Rat Bamphen Road as part of an ongoing crackdown on illegal foreign business activities and immigration-related offences.
Authorities initially identified three areas of suspected legal violations.
Suspects who were arrested at the scene were handed over to Huai Khwang police for legal action, he added.
In one case, four companies were found to be operating from the same address, and just one company was engaged in business activity legally, the DBD said.
