Online clothing giant Boohoo has said it is not "aware of any investigation" by US authorities after reports it could face an import ban.
Campaign group Liberty Shared said it had raised concerns with US customs about potential labour abuse in the company's supply chain.
Boohoo came under fire last year after reports factory workers at Leicester suppliers were being underpaid.
But it said it was "confident" it could meet customs standards in the US.
According to Sky News, US Customs and Border Protection (CBP) has seen sufficient evidence to launch an investigation after petitions from lawyer Duncan Jepson, who runs Liberty Shared, an NGO (non-governmental organisation) against modern day slavery.
In September a report by a barrister hired by the company found it had "capitalised on the commercial opportunities offered by lockdown" but took no responsibility for the consequences for those making the clothes they sold.
However, it also found the company had not committed any criminal offences.
In a statement, Boohoo said: "Over the past eight months the group has been working closely with UK enforcement bodies.
"If the group were to discover any suggestion of modern day slavery it would immediately disclose this to the relevant authorities."
The BBC has contacted the CBP in the US for comment.