The 122-page report offers a glimpse of working life at the factories, and also shows how conditions can be worse at Samsung's suppliers. For instance, base pay at Tianjin Intops, a supplier that employs 1,200 workers, is lower than at Samsung's own factories, and new hires receive no training. Workers' overtime at the factory reaches 100 to 150 hours per month depending on production needs.

China Labor Watch urged Samsung to launch third-party audits of its factories and to create hotlines for workers to express grievances.

Samsung couldn't immediately comment on the report Tuesday as it had not had time to study it. In its response Monday to the earlier report, Samsung said it has a "zero tolerance policy" for child labor and that it was establishing an "urgent and broad plan" to ensure its factories and suppliers' factories conform to local labor laws and to Samsung's policies.