Samsung says that an external audit found labour violations at dozens of its suppliers in China, including failure to provide safety gear and excessive working hours, but that none involved child workers.
The findings covered 100 of its Chinese suppliers - which number over 200 - and were outlined in its annual corporate social responsibility report.
"A majority of suppliers do not comply with China's legally permitted overtime hours," says page 69 of the report (PDF), saying that it demanded those suppliers reduce overtime.
The report is part of growing pressure on the world's two biggest smartphone suppliers, Apple and Samsung, which rely on Chinese labour to produce millions of phones every quarter. Apple was the focus of intense scrutiny from 2010 over labour practices at Foxconn, its principal supplier in China.
Samsung has already come under fire in its home country of south Korea over its response to claims that chemicals in one of its chip factories caused leukaemia and led to the deaths of a number of workers.
The company has apologised for the length of time it took to provide compensation, while saying that it does not accept there was a link.
The world's largest maker of mobile phones and smartphones, Samsung has been subjected to increasing examination of its practices. In 2012 it faced allegations that its plants in China used child labourers. New York-based pressure group China Labor Watch claimed that working conditions at Samsung suppliers were "inhumane", and the company vowed to eliminate illegal overtime by the end of 2014.
The latest report says that 33 suppliers broke local regulations on insurance, 39 paid fixed wages without compensation for overtime, and 33 cut pay as a disciplinary measure. The report doesn't specify the extent to which those figures overlapped.
The audit, covering the period to the end of December 2013, also found that 59 suppliers in China didn't provide sufficient protective goggles, masks and other safety equipment to workers, while 48 let minors (employees aged 16-18) handle chemicals. Most of the audited factories did not comply with legally permitted overtime hours.
The audit also found suppliers which had excessively noisy or dusty workplaces, and which failed to control air and water pollution from their output.
Samsung conducted its own audit of Chinese suppliers in 2012 and said it found instances of Chinese workers working beyond legal hours.
The audit was carried out by a third party auditor certified by the Electronic Industry Citizenship Coalition, an electronics industry group.
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