More than 20 Cambodians trafficked to work as illegal fishermen have been rescued from Thai fishing boats near Mauritius, officials said Wednesday.

Cambodia’s Ministry of Foreign Affairs said it had rescued 23 men on Thai boats fishing illegally in the Indian Ocean.

“With cooperation from Mauritius authorities, 23 Cambodian laborers were rescued when Thai fishing boats illegally fished in Mauritius’ maritime territory,” Koy Kuong, spokesman for the Ministry of Foreign Affairs, said in a statement.

Interior ministry official Chiv Phally told AFP they were investigating how the men ended up on Thai fishing boats. The Ministry said it is closely working with the International Organization for Migration to repatriate the victims to Cambodia.

Rights campaigners believe thousands of Myanmar and Cambodian men have been trafficked into Thailand’s huge fishing industry, reports AFP. Thailand has been placed on a US State Department trafficking in persons “watchlist” for two years running.

Tens of thousands of trafficked Cambodians are forced to work as fishermen on Thai boats and sail for months or even years without pay, according to Global Post. They are often reportedly physically and psychologically abused but unable to seek protection from the authorities in Thailand or abroad because they have no legal documents.