Thousands of Cambodian migrant workers in Thailand are rushing back across the border, voluntarily repatriating themselves in the face of increasingly hostile rhetoric towards undocumented labourers.

In the wake of Thailand’s coup d’état last month, army chief General Prayuth Chan-o-Cha urged better regulation of the workforce and warned illegal workers of their tenuous and unwelcome status, last week outlining ways “to prevent [an] illegal work force from entering into the country and give more work opportunities to Thai nationals”.

In response, many undocumented and unregistered Cambodian workers are deciding to show themselves the door. Border officials said groups of workers are cramming into military trucks, opting to be sent home rather than incur potential punishment.

“They are scared and decided themselves to come back. One day, around 100 or more came with Thai military transporting them to the border,” said Colonel Chin Piseth, deputy director of the Cambodian-Thai border relations office in Poipet.

Piseth estimated that thousands of Cambodians have returned since last week when the Thai military announced it would not take responsibility for any incident involving undocumented migrants.

While forcible expulsions from Thailand are not uncommon – a UN study found more than 89,000 Cambodians were deported from Thailand in 2009 for illegal migration – en masse voluntary returns or large round-ups of employed workers is extremely unusual, according to Moeun Tola, head of the labour program at the Community Legal Education Center.

“The military government has made it clear they want to control the situation with illegal workers. I’m not sure if they are worried Cambodians will join the ‘red shirt’ uprising or what,” he said.

“Before, a worker could be arrested and fined or deported, but now they can also be shot and killed. It’s gotten even more dangerous for migrant workers, and there’s no priority to improve the situation for them.”

Border officials said many of the daily returns include dozens of minors, summoned home by worried relatives.

Adding to the fears, Thai media have reported a rising number of arrests and crackdowns on migrant workers following the coup, with numbers particularly high over the past few days, according to Andy Hall, a migration expert based in Thailand and Myanmar.

“However, generally in my experience, police and law enforcement arrest, extort money from workers and their employers, and then simply release them unless they need to prove a deportation quota,” he said, adding that it is economically unviable for Thailand to send home all of its hundreds of thousands of undocumented workers.

Cambodian border police, meanwhile, claim the number of workers crossing has dwindled to almost none, and they intend to keep it that way.

“If we find them, we will not let them go, because we fear the danger,” said So Channary, commander of Border Police Infantry Unit 911.