Jingyu Toy Products, a toy factory based in the Chinese city of Shenzhen, has been accused of underpaying its employees and forcing them to work long hours, according to a report released by China Labor Watch (CLW) on Tuesday. Workers at the factory, which is a supplier to American toy companies, Hasbro and Mattel, and Japanese toy-maker Takara Tomy, recently went on strike, demanding compensation as the company prepared to relocate the plant.

As part of the investigation, CLW interviewed some factory workers who claimed that the company demanded that workers start a normal morning shift despite making them work until 2 a.m. the previous night. The workers also alleged that they were paid the local minimum wage of $327 a month, for 6 hours and 40 minutes on each weekday, though they sometimes worked for 12 hours a day to meet a sudden surge in orders.

“The normal daily shift—calculated as normal working hours—is only 6 hours and 40 minutes long rather than 8 hours,” the CLW report said. “In this way, a number of working hours paid at the normal workweek rate are shifted onto Saturdays, thereby allowing the company to avoid paying workers hours of weekend overtime pay each week.”

According to the workers, about 100 people participated in the strike last week, demanding severance pay and retirement insurance as Jingyu prepared to relocate the factory.

“New workers at Jingyu receive social insurance, but according to interviewees, the monthly individual insurance payment is 160 RMB ($26), which may indicate underpayment of insurance,” the report said, adding that some veteran workers are still waiting to be paid by the company for past insurance contributions.

CLW has in the past revealed excessive working hours and wage theft at Chinese toy factories. Between June and November 2014, CLW investigated labor conditions at four facilities in Guangdong province in southeast China and found several violations of labor rights, including hiring discrimination, detaining of personal IDs, a lack of physical exams and safety training, and excessive overtime work and unpaid wages.

China is currently dealing with a worsening labor shortage. Chinese media reported in April that local police detained more than 5,000 illegal foreign workers in southern Guangdong Province. According to the Guangzhou Daily newspaper, most of these people were in their 20s and 30s from neighboring countries in Southeast Asia.

Technology giants like Apple and Samsung also have been scrutinized in the past for working conditions in their suppliers' manufacturing units in China. According to an investigation conducted by CLW and Green America in August last year, Catcher Technology, a Taiwan-based supplier of aluminum enclosures for Apple’s iPads and MacBooks, violated 22 labor rights. Apple subsequently dispatched a team to investigate claims of unsafe labor practices at the company.