Lawmakers in Thailand have approved a measure creating tougher penalties for violating the country’s laws against human trafficking.

The legislation had been under debate for several weeks. But its passage comes in the wake of an Associated Press investigation published this week. It found that fish caught by slaves has entered the supply chains of major supermarkets, restaurants and even pet stores in the United States. Seafood that was caught by hundreds of men trapped on a remote Indonesian island was tracked to exporters in Thailand who sell to America.

Thailand’s deputy prime minister is denying that there are any slaves working on fishing boats carrying flags of Thailand. Instead, he says the problems are taking place in Indonesia.

But the U.S. State Department blacklisted Thailand last year for failing to meet minimum standards in fighting human trafficking.

U.S. retailers and the National Fisheries Institute have written to the ambassadors from Thailand and Indonesia, demanding to know what will be done to free the slaves described in AP’s coverage. They say they’ve asked the government of Thailand in the past to address the issue of forced labor — but didn’t have any specific allegations until now.

National Fisheries Institute spokesman Gavin Gibson says the commercial fishing industry in the U.S. opposes the use of slave labor in Asia.

Kamonpan Awaiwanont, who’s a spokesman for Thailand’s department of fisheries, says efforts are underway to stop the use of slave labor in the fishing industry.

The Associated Press