The report found that shrimp processed in plants using forced and child labor in Thailand was products sold in the US, Europe and Asia.
One of those plants allegedly supplied a subsidiary of Thai Union, AP reported.
Many workers have been tricked or sold to factories where they are forced to work long hours for little or no pay, the agency said.
US politicians have called for a boycott of the products, while Greenpeace called on the company and the Thai seafood sector to do more on the issue.
"Any illegal or unethical labour practices are unacceptable to Thai Union," Thai Union's chief executive Thiraphong Chansiri said.
"This is yet another wake up call not only to us, but to the entire industry."
The news comes as Thailand faces pressure from the European Union to clean up in another problem area in the industry - illegal fishing - or face a trade ban.
Thai Union's subsidiary Okeanus had terminated its relationship with a supplier it suspected of breaking its code of conduct, the company said in the statement.
Thai Union, which counts Wal-Mart and Costco Wholesale among buyers, said last week it had decided to stop working with external shrimp processing plants.
It would bring those operations in-house from Jan. 1, because it was difficult to guarantee external suppliers were following its rules, Thai Union said. The company would offer jobs to a thousand of the workers from those external processing plants.
Greenpeace called on the Thai Union to do more.
"The inaction by the entire industry and shiny PR moves are no longer acceptable," Greenpeace US oceans campaign director John Hocevar said.
"It is time for Thai Union and its buyers to audit and clean up every single link in their seafood supply chains - not just the one implicated in the latest of many investigations."
Thailand, the world's third-largest seafood exporter, was given six months by the European Union in April to address issues that had allowed fish caught illegally to enter the supply chain.
The US State Department said in a report this year on human trafficking that some Thai and migrant workers were subjected to forced labour on Thai fishing boats.
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