A coalition of civil society groups said on Thursday that major retailers must stop sourcing from the Xinjiang region due to the "grave risk of forced labour".
More than 180 organisations urged brands to end sourcing of cotton and clothing from the region and cut ties with any suppliers in China that benefit from forced labour.
The pressure comes after drone footage was posted anonymously on YouTube last year, showing hundreds of prisoners tied up and wearing blindfolds in Xinjiang, leading to speculation they were being transported to concentration camps.
The United Nations experts estimate that at least a million Uighurs and other Muslims are held in detention centres in Xinjiang.
But China has denied mistreatment, saying the the camps offer vocational training and aim to fight terrorism and extremism.
Last week, the Chinese ambassador to the UK dismissed allegations of abuse against the Uighur people after the BBC's Andrew Marr confronted him about the shocking drone footage.
The United States this month hit senior Chinese officials with sanctions over alleged rights abuses against the Uighurs.
Britain and France have also recently condemned their treatment.
The rights group said in a letter that many of their supply chains are likely to be tainted by cotton picked by Uighurs.
It said that while most fashion brands do not source directly from factories in Xinjiang, the cotton that is exported across China and used by other suppliers.
More than 80 per cent of China's cotton comes from northwestern Xinjiang, which is home to about 11 million Uighurs.
"Brands and retailers recognise there is a massive problem in the region, and that their supply chains are exposed to a grave risk of forced labour," said Scott Nova, head of the US-based Worker Rights Consortium (WRC), which signed the letter.
"We are cautiously optimistic that there will be commitments (from brands to pull out of Xinjiang) in the future," he added.
The Chinese embassies in London and Washington did not respond to requests for comment about the campaigners' letter.
A spokesperson for the Chinese embassy in the United States earlier this month said the accusation of forced labour in Xinjiang was "both false and malicious".
Meanwhile, the Thomson Reuters Foundation sent emails to more than 30 leading global retailers to ask about their supply chains in China and the origins of the cotton they sourced
Almost all of the brands did not respond directly to the questions, but most said they had anti-forced labour policies and required their suppliers to comply with a code of conduct.
Only one retailer - US-based Costco - declined to comment.
All the companies that responded - including Gap, Patagonia and Zara-owner Inditex - said they did not source from factories in Xinjiang.
However, the majority could not confirm that their supply chain was free of cotton picked from the region.
Japanese retailer Muji said it used cotton from Xinjiang but that independent auditors had found "no evidence of accusations of forced labour ... at their mills".
US-based PVH - owner of brands from Calvin Klein to Tommy Hilfiger - said it would cut ties with any factories or mills that produce fabric or use cotton from Xinjiang within a year.
"The only way brands can ensure they are not profiting from exploitation is by exiting the region and ending relationships with suppliers propping up this Chinese government system," said Jasmine O'Connor, chief executive of Anti-Slavery International.
Better Cotton Initiative (BCI), a global non-profit aiming to improve conditions in the garment sector, said in March it would no longer license so-called Better Cotton from Xinjiang.
Companies such as IKEA and H&M, who use BCI to source cotton, have previously said they backed the decision to suspend licensing in the region and would no longer source from there.
Amid the growing international pressure on China, the US government this month in a rare move said it blocked an $800,000 shipment of hair extensions from a Xinjiang-based business on suspicions that the goods were made with forced labour.
A New York Times investigation last week found some Chinese companies making face masks to protect against the coronavirus for both domestic and export markets had used Uighur labour.