Thousands of Muslim migrant workers from Burma risk being fined and deported from Thailand after June 30, under a new law that campaigners say may increase abuse and trafficking.

Under Thai regulations issued last year, migrant workers have until Saturday to register, using a Certificate of Identity issued by their home country, as a first step toward applying for a work permit.

But Muslims from Buddhist-majority Burma face major challenges getting documentation, said Kyaw Win, executive director of advocacy group Burma Human Rights Network (BHRN), which uses the former name for the country.

“These are people who fled Myanmar to escape persecution and civil war. This law increases their vulnerability,” he said.

“Their statelessness is an urgent and serious issue. If they cannot live in Thailand after June 30, they may have to return to Myanmar, where they face persecution and imprisonment,” said Kyaw Win, who conducted a survey of Muslim migrant workers.

Burma’s home ministry did not immediately respond to an e-mail requesting comment.

Since taking power in a 2014 coup, Thailand’s ruling junta has taken steps to regulate the foreign workforce, spurred partly by reports that unregulated workers faced exploitation by employers.

Thailand has more than 3 million migrant workers, according to the International Organization for Migration, although rights groups put the figure higher, as many are undocumented.

Since the labour regulation was announced, tens of thousands of migrant workers from Cambodia, Burma and Laos have fled Thailand, immigration officials have said.

Thousands of Muslims from Burma who remain in Thailand without the identity certificate, face fines of 2,000 to 100,000 baht ($60 to $3,000), five years in prison or deportation, and a two-year ban on re-applying for a work permit.

BHRN’s survey of Muslims from Burma in the Thai border town of Mae Sot found nearly 80 percent had never been issued citizenship documents.

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Two out of three had their applications for identity certificates rejected, their survey showed.

“Their very existence is denied,” Kyaw Win told the Thomson Reuters Foundation on Tuesday, at the release of the report.

“We are asking Thai authorities to adopt a humane policy towards them, and refrain from deporting them.”

Undocumented migrants may also face a greater risk of trafficking, as they will rely on brokers to get their documentation, or for jobs that do not require the certificate, said independent rights activist Johny Adhikari.

“It is ironic that a law that is meant to protect migrant workers may end up hurting them more,” he said.