Apple’s iPhone 6S’ may be a hit, but according to an industry watchdog, the Chinese workers who make them are still working under poor conditions to assemble them.

New York-based China Labor Watch made the allegations in a new report on Thursday, urging Apple to raise workers’ wages at a factory it investigated. The group has a long history of investigating the Cupertino company’s supply chain in China, and this time claims to have found problems at an iPhone factory in Shanghai.

The factory employs about 100,000 people and is from a subsidiary owned by manufacturing giant Pegatron, according to China Labor Watch. Apple’s own website lists the factory as building iPhones and iPads.

In September the facility was in its busiest period of the year, manufacturing Apple’s latest smartphones, the iPhone 6S and iPhone 6S Plus. During that time, China Labor Watch sent its own investigator to work undercover at the factory and learn about the conditions.

The investigator claimed that workers earn about $1.85 (AU$2.55 or £0.85) per hour, and pull significant overtime hours to make enough money to cover living expenses. The report further claimed that the standard shift was nine hours, but that — between September and December — staff worked an additional minimum of 20 hours of overtime each week, usually split up between an extra two hours each week day and one 10 hour shift on Saturdays. With overtime accounted for, the factory’s worker earn about $753 (AU$1,045 or £488) in monthly wages.

This overtime was essentially a requirement, according to the investigator, who claimed to be told by a trainer that working eight hour shifts five days a week “does not conform to our hiring requirements.”

Apple declined to comment on China Labor Watch’s report, though the Californian tech company regularly audits its suppliers, and releases its own annual reports that detail its progress in addressing any identified problems.

In recent years, the company has sought to cap the excessive work hours at the factories, with its guidelines for manufacturers stating a 60 hour maximum work-week. During 2014, 92 percent of the workers Apple monitored in its supply chain were complaint, according to the company, but in September of that year, when Apple was busy readying the iPhone 6 range for sale, the percentage fell to just over 75 percent for that month.

However, China Labor Watch found the compliance rate was lower this year at the Shanghai Pegatron factory, where the group collected pay stubs from 76 workers in September and found that only 42 percent of the employees had worked 60 hours a week or less.

It’s not the first time China Labor Watch has spoken out against working conditions in iPhone manufacturer factories, as the group in 2013 slammed Apple over low pay for the workers who make its devices.

The report also alleged that workers lived in cramped dorms, and that the factory failed to provide adequate job safety training.

The group did claim, however, that conditions had improved in a few areas — most notably, the hiring process. It claimed that in 2013 Pegatron was “explicitly” discriminatory against people over 35, people with dyed hair and those of Tibetan or Uyghur ethnicity, but none of that was present in 2015. There were also “partial” improvements in regards to sick leave and resignation, among other areas, according to the report.