The charity behind a pro-feminism T-shirt worn by leading politicians has vowed to investigate claims that the item was made in sweatshop conditions.
Equality campaigning group the Fawcett Society said it was "disappointed" to learn of the allegations.
The Mail on Sunday reported the £45 "This is what a feminist looks like" shirt is made by women paid 62p an hour on the island of Mauritius.
The Fawcett Society said it was told the garment would be made ethically.
The T-shirt has been worn by Deputy Prime Minister Nick Clegg and Labour leader Ed Miliband in promotional pictures - but Prime Minister David Cameron reportedly declined to be photographed in it.
Deputy Labour leader Harriet Harman then wore it in the House of Commons during Prime Minister's Questions.
BBC political correspondent Alan Soady said it was "definitely not what these three senior politicians would have wanted to see on the front page of the Mail on Sunday when they got up this morning".
'Ethical credentials queried'
The design of the Fawcett Society T-shirt was a collaboration with Elle magazine, which has described the garment as being part of an "ethically-produced" range.
High street chain Whistles was approached to design and produce the item, with all profits going to the charity.
Eva Neitzert, deputy CEO of the Fawcett Society, said they had been "assured that the garments would be produced ethically here in the UK".
She said in a statement: "Upon receiving samples of the range at our offices in early October we noted that the T-shirts had in fact been produced in Mauritius, upon which we queried (over email) the ethical credentials of the Mauritian factory, and the fabric used."
A reply from Whistles gave assurances about the T-shirts and sweatshirts - which had already been manufactured by then.
The Mail on Sunday toured one of six factories on Mauritius owned by Compagnie Mauricienne de Textile (CMT), which makes the garments, and claimed machinists slept 16 to a room.
The newspaper also alleged that women working at the factory make 6,000 rupees, or £120, a month - which the paper said was a quarter of the country's average wage.
A spokesman for Whistles told the paper: "We place a high priority on environmental, social and ethical issues.
"The allegations regarding the production of T-shirts in the CMT factory in Mauritius are extremely serious and we are investigating them as a matter of urgency."
The Fawcett Society statement continued: "We have been very disappointed to hear the allegations that conditions in the Mauritius factory may not adhere to the ethical standards that we, as the Fawcett Society, would require of any product that bears our name.
"At this stage, we require evidence to back up the claims being made by a journalist at the Mail on Sunday.
"However, as a charity that campaigns on issues of women's economic equality, we take these allegations extremely seriously and will do our utmost to investigate them."
'Unaware of origins'
If there is evidence that factory workers have been mistreated, the charity will ask Whistles to withdraw the range "and donate part of the profits to an ethical trading campaigning body".
Dr Neitzert added: "Whilst we wish to apologise to all those concerned who may have experienced adverse conditions, we remain confident that we took every practicable and reasonable step to ensure that the range would be ethically produced and await a fuller understanding of the circumstances under which the garments were produced."
Elle said the range, also including a phone case and clutch bag, had been created as part of its first feminism issue.
Celebrities including actors Benedict Cumberbatch, Joseph Gordon Levitt and Tom Hiddleston have been photographed wearing the T-shirt for the magazine.
A spokesman for the deputy prime minister said: "Nick Clegg had no idea where these T-shirts were being made and can only assume that the Fawcett Society were unaware of the origins, or they would not have asked him to wear it.
"He remains entirely supportive of efforts to ensure all women are treated as equals in this country and the world over."
A Labour party spokesman told the BBC: "It was a campaign run by Elle and the Fawcett Society to promote feminism and we were happy to support it."