Beyonce's new range of women's sportswear is made using sweat shop labourers who earn as little as £4.30 (NZ$9.13 ) a day, it has been reported.
The American pop star's Ivy Park gym gear is sold by Top Shop, the high street fashion retailer owned by Sir Philip Green, who is already facing criticism over the collapse of department store BHS.
The Sun on Sunday reported the clothing range - which Beyonce said she hopes will "support and inspire women" - is made by Sri Lankan seamstresses some of whom earn £4.30 (NZ$9.13 ) a day.
Workers are paid more than the legal minimum but campaigners described the labour as a "form of sweat shop slavery".
Top Shop has claimed the Ivy Park range will "empower women through sport".
One machinist told tabloid: "When they talk about women and empowerment this is just for the foreigners.
"They want the foreigners to think everything is okay."
A 22-year-old seamstress told the Sun on Sunday she earned 18,500 rupees (£87.260 (NZ$185.21) a month, which is about half the Sri Lankan average wage, for a nine and three-quarter hour shift, five days a week, plus overtime.
Beyonce, whose full name is Beyonce Giselle Knowles-Carter, said at the launch of the 228-piece clothing range: "My goal with Ivy Park is to push the boundaries of ¬athletic wear and to support and inspire women who understand that beauty is more than your physical appearance.
"True beauty is in the health of our minds, hearts and bodies.
"I know that when I feel physically strong, I am mentally strong and I wanted to create a brand that made other women feel the same way."
Beyonce and husband Jay Z, the rapper, are worth a combined £760 million (NZ$1613 million).
Jakub Sobik, from the charity Anti-Slavery International, said: "This is a form of sweat shop slavery.
"There are a number of elements here that tick the boxes in terms of slavery, the low pay, restriction of women's movement at night and locking them in.
"Companies like Topshop have a duty to find out if these things are happening, and it has long been shown that ethical inspections by these companies are failing. They should be replaced by independent inspections."
The Sri Lankan manufacturer making some of the Ivy Park garments is MAS Holdings, owned by tycoon Mahesh Amalean, 61, and his two brothers, which employs 74,000 workers in 48 factories across Asia.
A Topshop spokeswoman said: "Ivy Park has a rigorous ethical trading programme.
"We expect our suppliers to meet our code of conduct and we support them in achieving these requirements.
"We are proud of our sustained efforts in terms of factory inspections and audits, and our teams worldwide work very closely with our suppliers and their factories to ensure compliance.
"We expect our suppliers to meet our code of conduct and we support them in achieving these requirements."