The Environmental Justice Foundation (EJF) charged that Thailand is failing to address severe abuse of Myanmar-origin migrant workers in its fishing industry.

The British-based foundation said that the Thai government has failed to tackle "endemic corruption, poor enforcement, inadequate victim support, unacceptable working conditions and deficient migration policy" in the industry.

Labour Ministry Deputy Permanent Secretary Boontharik Samiti responded to the claims by insisting that the government was making a serious effort to protect fisheries workers.

"We are aiming to reduce and eradicate human trafficking. For fisheries, all agencies have come together in an effort to prevent this problem in a sustainable and long-term fashion," he asserted.

But the EJF suggested that the United States should consider imposing economic sanctions on Thailand.

According to the group, the value of US seafood imports from Thailand exceeded $1.6 billion (£1bn) in 2013.

Thailand's fishing industry is staffed predominantly by migrants from poorer neighbouring countries.

Often the workers arrive illegally with the help of human traffickers, leaving them little legal protection and large debts.

Very few have any sort of contract.

"Depending on the amount paid, a trafficked fisherman could often work from one to eight months before earning any wages for himself," noted a 2011 report by the International Organisation for Migration.

EJF director Steve Trent said: "Migrant workers in the fishing industry, many of them trafficked illegally, are suffering terrible abuses and are all too often denied basic human rights.

"These people are seafood slaves - forced to work to prop up the cash-rich fisheries industry."

Mr Trent added that unsound environmental practices worsen the problem. Overfishing has led to declining catches, so operators use the cheapest labour and keep workers at sea longer to make the catch.

The organisation said that its findings would justify the US State Department downgrading Thailand to the lowest ranking in its annual human trafficking report - a step that would subject it to automatic sanctions.

Thailand has been on a watch list for four years for planning reforms but failing to implement them.