Suppliers to several big clothing brands are polluting two of China's main rivers with hazardous chemicals, according to Greenpeace.
The new report by the environmental group raises questions about the companies Adidas, Abercrombie & Fitch, H&M and others do business with.
Greenpeace says they take advantage of China's lax environmental regulations.
It called on the companies to make sure their products did not damage the environment and public health.
Greenpeace said laboratory tests on samples collected from two major textile suppliers, in the Pearl River Delta in southern China and the Yangtze River Delta in Eastern China, over a period of a year revealed toxic chemicals in waste water.
The chemicals found at the Youngor Textile Complex near Shanghai and the Well Dyeing Factory near Hong Kong included nonylphenols, a subset of alkylphenols and perfluorinated chemicals (PFCs).
Alkylphenols and some PFCs are banned by the EU, although they are still widely used in the textile industry in developing countries such as China.
The chemicals have hormone-disrupting properties that can cause the feminisation of fish and reduced sperm count in men, the report said.
"Now we have scientific evidence confirming that hazardous chemicals are being released into China's rivers to make clothes worn by people around the globe," said Vivien Yau, a Greenpeace campaigner in Hong Kong, who was part of a team that compiled the report.
Her colleague, Gloria Chang, campaign manager, said that the report's findings were just the tip of the iceberg, as there were hundreds of similar textile suppliers in China.
China has been the world's largest textile exporter since 1995.
Greenpeace said the multinationals highlighted in the report had the power to persuade their suppliers to phase out the use of hazardous substances.
The group said that some brands like Nike, Adidas and Puma already had policies that restricted hazardous substances in their finished products and, to a lesser extent, their manufacturing process, but wastewater discharges were often overlooked.
The report said the brands that confirmed commercial relationships with the two suppliers investigated were Abercrombie & Fitch, Adidas, Bauer Hockey, Calvin Klein, Converse, Spanish firm Cortefiel, H&M, Lacoste, Chinese brand Li Ning, Puma and Chinese casual wear firm Meters/bonwe.
However, when contacted by Greenpeace before the report was made public, Bauer Hockey, Converse, Cortefiel, H&M, Nike and Puma all said that they made no use of processes involving water of the Youngor Group in the production of their garments.
Adidas told the BBC that its business relationship with the Youngor Group was limited to the cutting and sewing of garments.
"The Adidas Group does not source fabrics from Youngor Group, which would involve the use of dyestuffs, chemicals and their associated water treatments processes," the company said.
Likewise, Puma, Nike and H&M told the BBC they acquired fabric from outside the Youngor Group and did not use Youngor for any industrial processes that discharge water into the river Fenghua.
Lacoste told Greenpeace it took the matter seriously and would investigate it.
The BBC contacted the other brands named in the report, but they did not respond immediately to calls for comment.