Online fashion retailer Boohoo says it will investigate the use of a factory in Leicester after concerns were raised by a government minister following allegations in a newspaper.
The Manchester-based firm is looking into how its items came to be produced at Jaswal Fashion factory.
The retailer claims the factory had not been one of its 'direct suppliers'.
Allegations about the factory's running have prompted an investigation by the National Crime Agency - and have been labelled 'appalling' by Home Secretary Priti Patel.
Leicester has been the first UK city to impose a local lockdown following a dramatic spike in coronavirus cases over the past few weeks.
Health Secretary Matt Hancock said the city had seen outbreaks in food and clothing factories, prompting 'significant concerns' about the employment practices of some firms.
Boohoo said in a statement that Jaswal Fashions is 'not a declared supplier' and that it 'appeared that a different company is using Jaswal’s former premises'.
"We are currently trying to establish the identity of this company," the statement added.
"We are taking immediate action to thoroughly investigate how our garments were in their hands, will ensure that our suppliers immediately cease working with this company, and we will urgently review our relationship with any suppliers who have subcontracted work to the manufacturer in question."
Home Secretary Ms Patel raised concerns following a Sunday Times investigation.
On Friday, Leicestershire Police said they had carried out routine visits at nine workplaces in the city of Leicester, to ensure health and safety.
The NCA said in a statement: "Within the last few days NCA officers, along with Leicestershire Police and other partner agencies, attended a number of business premises in Leicester area to assess concerns of modern slavery and human trafficking."
Nasty Gal told the Sunday Times that the company would investigate the claims but said the factory is not a "direct supplier."
On Monday, Boohoo said: "We are keen and willing to work with local officials to raise standards because we are absolutely committed to eradicating any instance of non-compliance and to ensuring the actions of a few do not continue to undermine the excellent work of many of our suppliers in the area, who provide good jobs and good working conditions."
