President Barack Obama has signed a bill barring the import of goods produced by forced labour from entering the US, throwing the weight of the US market into the fight against global slavery.
Shipments derived from slavery, from fish to electronics and cocoa, will be kept out of the country under the new law that closes a legal loophole that allowed import of goods derived from forced labour if US demand exceeded domestic production, officials said.
The measure closing the loophole from the Tariff Act of 1930 was included in a wider trade enforcement bill, which Obama signed into law at the White House on Wednesday.
"The mere deterrent effect of closing this loophole is a great step forward," Gil Kerlikowske, commissioner of US Customs and Border Protection, told reporters on a conference call. "We're going to make sure that is heavily noted throughout the world."
Only a few countries have laws addressing forced labour goods, including Canada where prison-labour imports are illegal and Australia where financial benefits from forced labour are outlawed, according to the US Department of Homeland Security.
The new law could keep at bay billions of dollars worth of goods produced by forced labour, said Annick Febrey, senior associate at the advocacy group Human Rights First.
"It's a really big deal," she said. "While we as a country have said that we are against slavery, we've had this little-known rule in the Tariff Act."
The International Labour Organisation estimates that 20.9 million people are victims of forced labour globally.
The illegal industry is estimated to generate US$150 billion ($A208.15 billion) in profits per year, the agency has said.
Implementation of earlier US anti-slavery measures faltered because of a need to determine if demand exceeded domestic production, Febrey said.
Enforcement of the new law should benefit from data from the US Department of Labour, which has been listing goods, classified by nation, that are likely made by forced labour, officials said.