Ninety-seven foreigners had been arrested in the northeast for overstaying their visas or working illegally, Immigration Police acting regional director Maj General Natthawat Kandee told a press conference on Thursday.
Some had stayed illegally in Thailand for over a decade, he said, warning employers of serious punishments for hiring illegally.
Under Operation Zero Overstay, police on Wednesday searched Nong Khai, Ubon Ratchathani, Mukdahan, Nakhon
Phanom, Loei, Si Sa Ket, Nakhon Ratchasima, Surin, Bung Kan, Khon Kaen, Udon Thani, Sakhon Nakhon, Amnat Charoen, Roi Et, Maha Sarakham, Chaiyaphum and Buri Ram.
Those detained were mostly Indian, Laotian, Cambodian and Vietnamese with 27 overstaying their visas and 43 entering illegally. Nine worked without permission and two had not notified the authorities about their accommodation.
Police also charged 13 Thai homeowners for failing to notify the authorities about foreigners staying with them and three employers for taking on staff illegally, he added.
Natthawat said immigration police were also partially to blame for not performing proper checks.
He said crackdowns would continue periodically until they achieved Deputy Prime Minister Prawit Wongsuwan's goal of expelling all overstaying foreigners.
He said overstaying foreigners, once off the authorities' radar, were more likely to commit crimes such as fraud.