Thai officials insist the movement is voluntary and not forced repatriation. However, Thailand announced it would crack down on undocumented foreign workers after the army took power in a 22 May coup.
Cambodian rights groups claim Thai authorities are coercing the Cambodians to leave.
There are estimated to be more than 200,000 Cambodians working in Thailand, most illegally. Cambodian foreign ministry spokesman Koy Kuong said more than 160,000 have returned home through several border checkpoints since 1 June.
The trigger for the exodus seems to have been comments by Thailand’s military government that it would crack down on illegal immigrants and those employing them. Several were reportedly fired from jobs and sent home, and the belief spread that both legal and illegal workers were being ejected.
The military’s ruling National Council for Peace and Order (NCPO) insists Cambodians are leaving of their own accord and said 60,000 had crossed the border as of Saturday.
Roads leading to the border were packed on Sunday with trucks and buses full of Cambodian workers opting to head home rather than face any confrontation with Thai authorities.
NCPO spokesman Winthai Suvaree said: “The NCPO has no policy to sweep and clean, but teams must go to areas where there are illegal labourers to organise and manage the foreign workforce as we have accumulated problems over the past ten years.
“We ask that those who employ foreign workers continue their activities as normal and maintain good order.”
Mr Kuong said: “We request that [Thailand] send workers [back to Cambodia] in a humanitarian way, or without prosecuting, and facilitate the legalisation of undocumented workers.”
The exodus could prove disastrous for the Thai economy, which relies heavily on foreign workers – mainly from Laos, Cambodia and Burma – to perform jobs most Thais are reluctant to do, including manual labour and domestic work.
Army chief General Prayuth Chan-ocha seized power in Thailand in a bloodless coup following six months of street protests aimed at overthrowing prime minister Yingluck Shinawatra.
Her brother, former premier Thaksin Shinawatra – ousted by the military in a 2006 coup – was seen by many as the power behind the Yingluck government and was the most divisive politician in recent Thai history.
Despite a long history of enmity between the two countries, Cambodia’s veteran leader, Hun Sen, became a close ally of Thaksin during his years as premier.
Several leaders of the pro-Thaksin “red shirt” movement have sought refuge in Cambodia after turmoil in Thailand.