Dec. 14 last day for obtaining work permits
"After today, those who work in Thailand illegally will have to travel back to their countries and they can only return through legal channels," said Dechar Peukpattanaruk, director of the Office of Foreign Workers Administration.
Thailand, Southeast Asia's second-largest economy, is heavily dependent on migrant workers. People from Myanmar cross the porous border to fill a shortage of workers and — even after their country's recent opening-up — to escape unemployment.
Thai employers' groups had called for the deadline to be pushed back, fearing a shortage of manual workers in an already tight labour market.
The national verification program requires migrants to get temporary passports at home in order to renew or apply for Thai work permits.
If granted legal status, they are given the same labour rights as Thai citizens, including a 35 per cent minimum wage increase for those working in some regions starting in January.
But rights groups say the verification system is corrupt and leads to situations of debt bondage amounting to forced labour.
"After Friday it's going to turn into a corruption fest, an abusive situation where officials extort illegal workers, and migrants are not the only ones who will suffer — Thai employers and Thailand's economy will as well," said Andy Hall, a migration expert at Mahidol University in Bangkok.
Between two million and 2.5 million migrant workers from neighbouring countries including Myanmar, Laos and Cambodia live in Thailand, according to a 2011 government census.
About 80 per cent of them are from Myanmar, most in labour-intensive industries such as seafood processing and garments, and their unregistered status leaves them vulnerable to abuse.
Data from the Labour Ministry shows only 743,963, less than one-half of all migrant workers, have gone through the verification process.
Labour activists say the system is flawed and up to 1.5 million unregistered Myanmar migrants are not eligible for verification in the first place, since some, including Muslim Rohingya people, are denied citizenship by Myanmar.
Many migrants will try to remain in Thailand, said Hall.
"There won't be a mass exodus because Myanmar certainly can't offer jobs right now to those hailing from rural areas," he said.