Thailand is cracking down on migrant workers, saying they are stealing jobs from locals and should only have menial jobs.
The raids come amid growing anti-immigrant sentiment and economic stagnation in Thailand which is Southeast Asia’s second-largest economy.
"We have received many complaints about illegal immigrants working in markets including Vietnamese and even South Asians who were stealing jobs from Thais," Thai immigration police chief Nathorn Phrosunthorn told Reuters.
"They should be doing the jobs that Thais don't want to do like work as house cleaners.”
International Organisation for Migration figures show that more than three million migrants work in Thailand, the majority of them are from Myanmar.
Thailand’s economy between the 1980s and 1990s boasted annual growth rates of over 7 percent, drawing workers from neighbouring countries and other parts of Asia.
Migrants mostly did jobs Thais tend to spurn, including backbreaking work in the fishing and construction sectors.
For example, a 2015 memorandum of understanding, between Thailand and neighboring states, limits the fields in which Vietnamese citizens can seek employment. The memorandum allows them only to work as manual labourers in Thailand’s fishing or construction sectors.
More than two years of military rule and a shaky economy, which is on course to grow only three percent in 2016 after expanding 2.8 percent in 2015 and only 0.7 percent in 2014, are contributing factors to rising resentment towards migrants.
"There seems to be a surge of national sentiment in Thai immigration policy claiming migrants from Vietnam, for example, are taking jobs that are reserved for Thai nationals," Sunai Phasuk from Human Rights Watch told Reuters.
"We haven't seen this kind of rise in anti-immigrant sentiment for decades. This has a lot to do with economic concerns."
But locals say migrants are fighting for the same jobs as Thais and that some of them need to be sent back.
Raids conducted between September 1 and September 26 saw 153 migrants detained according to labour department figures. Those caught face up to five years in prison, a fine of up to 3,000 baht ($100) or deportation.
Human trafficking rings target migrants and sell them into virtual slavery on plantations, timber mills and fishing boats, human rights groups say.
The US State Department removed Thailand from the bottom tier of its annual list of worst human trafficking offenders this year, but the department says “widespread forced labour” still exists in the country’s vital seafood industry.