Amazon has been criticised over conditions at a Chinese factory that produces Kindles, Echo Dots, and tablets.
A China Labour Watch detailed illegal numbers of temporary workers, as well as staff being underpaid and overworked.
Amazon said it has "immediately requested a corrective action plan" after uncovering violations at the Hengyang Foxconn plant.
Amazon has been criticised by China Labour Watch over the conditions for workers at a factory that produces the company's Kindles, Echo Dots, and tablets.
In a nine-month investigation into working practices at the Hengyang Foxconn factory in China's Hunan province, China Labour Watch produced a 94-page report detailing illegal numbers of temporary workers, as well as staff being underpaid and overworked.
Responding to the report, titled "Amazon Profits from Secretly Oppressing its Supplier’s Workers," Amazon said it recently identified "two issues of concern" during a supplier audit at Hengyang Foxconn and "immediately requested a corrective action plan."
During interviews with 20 employees, China Labour Watch found that 2,000, or 44% of Hengyang Foxconn's total workforce of 4,500 were "dispatch" employees, who work on temporary contracts. This, it said, was a "clear violation" of Chinese laws mandating that only 10% of staff be on dispatch contracts.
China Labour Watch said dispatch staff were paid less than permanent staff, had significantly less training, were not properly rewarded for working overtime, and were not paid for sick leave. Dispatch workers earned 14.5 yuan ($2.26/£1.69) an hour, it said.
The investigation also found that during peak production times, factory staff were working more than 100 hours of overtime a month — nearly triple the 36 hours of overtime a month permitted under Chinese law. There was also "an instance" of employees working 14 consecutive days without a day off.
Furthermore, China Labour Watch said dormitories, where workers live, did not have emergency exits and bathrooms were in a state of disrepair.
An Amazon spokesman said: "Amazon takes reported violations of our Supplier Code of Conduct extremely seriously. Amazon regularly assesses suppliers, using independent auditors as appropriate, to monitor continued compliance and improvement.
"In the case of the Foxconn Hengyang factory, Amazon completed its most recent audit in March 2018 and identified two issues of concern. We immediately requested a corrective action plan from Foxconn Hengyang detailing their plan to remediate the issues identified, and we are conducting regular assessments to monitor for implementation and compliance with our Supplier Code of Conduct. We are committed to ensuring that these issues are resolved."