The British fast-fashion retailer Boohoo has been again forced to defend supplier practices after a report said it faces a potential U.S. import ban due to slave labor allegations.

The U.S.’ Customs and Border Protection (CBP) has seen enough evidence to start a probe after petitions from lawyer Duncan Jepson, who runs the campaign group Liberty Shared, Sky News reported.

“The evidence of Boohoo and forced labor is quite compelling. I think it will be a wake-up call for British institutions about how they’re handling modern slavery-enforced labor, particularly in a community like Leicester East,” Jepson is quoted as saying.

Boohoo said it has not been notified of any investigation by CBP.

“We are confident in the actions that we are taking to ensure that all of the group’s products meet and exceed the CBP criteria on preventing the product of forced labour entering the U.S.,” it said in a statement.

Last September, Boohoo accepted all the recommendations of an independent review which found major failings in its supply chain in the textiles hub of Leicester, England, sparked by newspaper allegations about working conditions and low pay.

According to Boohoo, it has enacted a series of measures to control its supply chain which include appointing Bureau Veritas and Verisio to support the ethical audits of suppliers and subcontractors. It claims that over 400 on-site audits were completed on British suppliers. It has also strengthened its internal responsible sourcing, compliance and sustainability teams as well as established a supply chain compliance committee reporting to the board.

The company said that it has removed 64 suppliers from its U.K. supplier list because they did not meet its standards on transparency.

It is also committed to publish a list of tier one and tier two British suppliers by end of March and a list of global suppliers by the end of September. Both lists will be updated every six months.

But, the broker Liberum noted that “concerns over working conditions across the group’s supply chain linger and now for the first time we see a major risk towards revenues.”