A supplier for Samsung Electronics isn't paying some overtime to workers at its mobile-phone factory in southern China, according to a report from labor-rights group China Labor Watch. Following an undercover investigation, China Labor Watch (CLW) has published a report on the labor conditions at a Samsung cell phone supplier, revealing labor rights violations that include $84,000 of monthly unpaid overtime wages, up to 148 hours of overtime per month, intense rates of work that have workers assembling one cell phone case every four seconds, regular verbal abuse by management, forcing workers to work barefoot, fines imposed on workers, and insufficient safety training and safety measures. Samkwang Science & Technology Co. in Dongguan also violated Chinese labor laws by discriminating against men, pregnant women, ethnic minorities and applicants older than 39, the New York-based group said in a report on its website today.

In September 2013, CLW sent an investigator into Samkwang Science and Technology in Dongguan, China to work on the production line for two weeks. Producing cell phone covers, phone screens, and other parts for Samsung, the Samkwang factory employs over 5,000 workers.

China Labor Watch has also investigated working conditions at Apple supplier.

Last year, the group said a Chinese supplier of mobile-phone covers to Samsung employed girls under the legal working age of 16 in China. The group also found instances of forced overtime at HTNS Shenzhen Co. and said tightly shut windows resulted in poor air quality and a lack of proper ventilation.

Apple assembler Foxconn Technology Group, the world?s largest contract manufacturer of electronics, said in October it was investigating practices at its Yantai plant in China after interns worked overtime in breach of company policy.