BANGKOK • Tougher penalties to punish Thai employers who hire illegal foreign workers have started, but the authorities will give a grace period of several months before imposing the new fines of between 400,000 baht (S$16,200) and 800,000 baht for each immigrant employed.

Foreigners found working without a work permit face fines of between 2,000 baht and 100,000 baht, or imprisonment of up to five years.

The ruling started on June 23.

Employment Department director-general Waranon Pitiwan said on Thursday that the authorities will not arrest illegal workers during this period, but allow employers to send them to get passports, visas and registration.

He said manpower shortages in the construction sector, and for those working as maids in homes and small and medium-sized enterprises could be expected in the first few months of implementation.

There are an estimated three million illegal foreign workers in the country, with one million believed to be from Myanmar.

The decree aims to raise the standards of foreign labour recruitment, and was in response to criticisms on human trafficking from the international community.

In the 2017 Trafficking in Persons report released this week, Thailand remained on the Tier 2 watch list, with the United States' State Department saying the kingdom had failed to meet minimum standards in addressing the issue.

Prime Minister Prayut Chan-o- cha has told the Ministry of Labour to help soften the impact of the new law amid concern that businesses would face acute manpower shortages.

Still, there has been a spike in the number of migrant workers deported daily from Thailand following the new ruling. Reports say that up to 200 Cambodian workers on average have been deported daily, while almost 3,000 from Myanmar have returned home since June 23.