The US has cut Swaziland from a lucrative duty-free trade programme because of concerns about crackdowns on peaceful demonstrations and poor protection of workers' rights.
Barack Obama, the US president, on Thursday said Swaziland was removed from the Africa Growth Opportunity Act because of its use of force against demonstrations and lack of recognition of labour unions
The act offers preferential access to the US market for goods from some 40 sub-Saharan nations that meet political and economic standards.
Swaziland's exclusion will raise the cost of its exports to the US.
The US trade representative, Michael Froman, said Washington hoped to work with Swaziland to improve conditions so it could return to AGOA.
"The withdrawal of AGOA benefits is not a decision that is taken lightly," Froman said in a statement.
"We have made our concerns very clear to Swaziland over the last several years and we engaged extensively on concrete steps that Swaziland could take to address the concerns."
The US reinstated AGOA benefits for Madagascar, which was dropped after a coup in 2009, following peaceful elections in the country.
US imports from Swaziland have steadily dwindled in recent years to $58.9m in 2013, most of it clothing. Madagascar shipped $179.8m in goods to the US in 2013.