A labour rights group said Thursday it had found "deplorable" conditions at Apple suppliers in China, following a probe of several firms that supply the US technology giant.
New York-based China Labor Watch said a four-month investigation of suppliers to Apple in southern and eastern China uncovered violations of workers' rights, including excessive overtime and hazardous work conditions.
"This investigation of ten different Apple factories in China finds that harmful, damaging work environments characterised by illegally long hours for low levels of pay are widespread in Apple's supply (chain)," the group said.
The lengthy report followed findings announced in March by the Fair Labor Association (FLA), which toured three Chinese suppliers with Apple's consent and also reported on forced overtime and other problems.
Executive director of China Labor Watch, Li Qiang, urged Apple to make good on pledges to improve, and in a letter to company chief executive Tim Cook called for immediate changes to be made.
"Are these promises sincere or merely a public relations ploy?" the report asked. "Apple is responsible for the existing problems in its suppliers' factories, instead of shirking its responsibility."
Following the FLA report, Apple's largest supplier, Taiwan's Foxconn, pledged to end workplace abuses at its factories in China, including overtime above the amount permitted by Chinese law.
Foxconn has come under scrutiny since 2010, following a spate of suicides and incidents of labour unrest at its Chinese plants.
At least 13 of its employees died in apparent suicides in 2010, with several more deaths last year.
China Labor Watch reported that other Apple suppliers had treated their staff worse than Foxconn, which has received the most attention.
"The labour rights violations at Foxconn also exist in virtually all other Apple supplier factories and in many cases are actually significantly more dire than Foxconn," the report said.
The group found employees worked an average of between 100 and 130 hours of overtime a month at the 10 factories, well above China's legal limit of 36 hours.
Low wages compelled workers to accept overtime and some factories did not properly compensate them for the hours, it stated.
Working conditions in factories that produce cases for Apple products were especially poor, the report said.
"Workers are often exposed to loud noise, toxic airborne particles and hazardous chemicals on a daily basis, and injuries while operating machinery are not uncommon," the report said.
The group took particular issue with the use of temporary workers hired through employment agencies, which allow companies to pay lower salaries and benefits.
"Dispatched workers are treated like second-class workers and their rights are regularly trampled on," it said.
Products of California-based Apple are wildly popular in China, where the iPhone and iPad are particularly coveted by wealthy consumers.
China Labor Watch said more than 70 percent of the workers it surveyed did not own Apple products but would like to have at least one.
The 10 companies investigated included Foxconn, Jabil Circuit and BYD Electronic in the southern city of Shenzhen, which borders Hong Kong, as well as Riteng Computer Accessory and Kenseisha in the commercial hub Shanghai.
In Jiangsu province near Shanghai, the group surveyed and interviewed workers at AVY Precision Surface Technology, Toyo Precision Appliance, Catcher Technology, United Win Technology and Tenglong Hardware.
Explore further: Out-of-patience investors sell off Amazon