Anyone know the reason for this?
Is it to be sure the Thai don't have to pay their fare home?

The Labour Ministry has issued a regulation requiring migrant workers to contribute to a repatriation fund starting from January 1.

The Employment Department's deputy chief Pravit Khiangphol said this meant that employers renewing their workers' work permits have to make six contributions to the fund at the Employment Office on the 1st and 15th of every month.
Burmese or Laotian workers are required to pay a total of Bt2,400 at Bt400 a month, while a Cambodian worker needs pay Bt2,100 at a Bt350 installation. The employer has to deduct the contribution from the workers' salary or risk getting fined 2 per cent of the contribution every month, he said.

If a migrant worker returns to his home country, he can withdraw the entire contribution, and if they don't and they come back to work in Thailand, they don't need to contribute again, he added.