A Chinese factory that provides parts to Apple, Dell and other hi-tech firms has been accused of violating safety rules and workers’ rights.

A report by non-profit China Labor Watch and Green America says 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 Suqian is run by Catcher Technology, a Taiwanese firm that mass produces light metal casings for smartphones, tablets, laptops and MP3 players. Its website says it works for hi-tech firms including Apple, Motorola, LG, Samsung, Sony and Dell.

The latest report, based on an undercover investigation, found that some conditions had deteriorated since a 2013 probe. Two years of broken promises notes that workers without the proper protective equipment suffer skin and eye irritation and are at risk of serious health problems, the investigation found. Some safety exits were locked, there was no safety training and there was “dense” dust in some workshops. There was also mandatory overtime of up to 100 hours a month, some unpaid.

“The health and safety violations found in this factory two years in a row are startling,” said Elizabeth O’Connell, the campaigns director at Green America who has led the ‘Bad Apple’ campaign. “The lack of fire drill training and locked safety exits are inexcusable in a work environment that requires the handling of flammable materials. Additionally, the lack of safety training in this facility and improper handling of hazardous materials contributes to the risk of life-threatening emergencies.”