A Chinese factory that provides parts to Apple, Dell and other tech firms has been accused of violating safety conventions and workers' rights.
A report by non-profit China Labor Watch and Green America alleged that labourers were exposed to toxic chemicals, given inadequate training, and made to pay for drinking water in their living quarters.
The plant employs about 20,000 people.
Apple said it had dispatched a team to China to investigate the report.
The facility in the eastern city of Suqian is run by Catcher Technology, a Taiwanese firm that mass-produces light metal casings for smartphones, tablets, laptops and MP3 players.
The company manufactured some iPad and Macbook components and its website indicates that it has done work with Motorola, LG, Samsung, Sony and Dell, among others.
After having raised concerns about the Suqian factory with Apple in 2013, the charities sent an undercover investigator to see if things had improved.
JUSTCLICK & CONNECT