Hong Kong-based Students and Scholars Against Corporate Misbehaviour (SACOM) said the strike erupted at a Foxconn factory in Fengcheng, Jiangxi province, Thursday, with over 1,000 workers taking to the streets the following day.
But electronics manufacturer Foxconn denied ownership of the plant, describing it as a "supply chain factory".
Foxconn, which assembles products for Apple, Sony and Nokia, has come under the spotlight in recent years after suicides, labour unrest and the use of underage interns at its Chinese plants.
And on Wednesday it said it was investigating and reviewing its acquisition procedures in China after allegations some of its managers had solicited bribes from suppliers.
SACOM spokeswoman Debby Chan said employees at the Fengcheng factory had complained of sweatshop-like conditions and poor pay.
"Workers mainly expressed their anger over the unfair treatment," she said.
A man who works at the Xinhua Hotel near the factory told AFP on condition o anonymity "At least 1,000 people attended the strike, several employees were taken away by the police, but I don't know how many."
Foxconn said the employee action ended Friday.
"This 'strike' involved more than 300 employees and continued until January 11," the company said, adding that most of the employees had returned to work.
Foxconn is the world's largest maker of computer components and employs up to 1.1 million workers in China.
In 2010, at least 13 Foxconn employees in China died in apparent suicides, which activists blamed on tough working conditions, prompting calls for better treatment of staff.
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