Last September, a young Chinese laborer named Shi Zhaokun began working long hours at a huge manufacturing plant here that produces Apple's new iPhone 5C.
But on Oct. 9, Mr. Shi was unable to make it to work and checked into a hospital, his family says. Soon after, he was pronounced dead of pneumonia. Although his identification papers said he was 20, Mr. Shi was in fact just 15.
In China, he was too young to legally work on a factory floor.
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Pegatron, the Taiwanese manufacturer that employed him, said the workplace environment at the Shanghai plant was not the cause of his illness. But a spokeswoman acknowledged that several other young workers at the factory had also died in the past few months.
Labor rights activists say Pegatron has failed to explain at least five deaths of young workers in recent months. They say workers interviewed by China Labor Watch, a nonprofit group that monitors working conditions in China, have complained about long working hours and harsh working conditions at Pegatron, including some of the same pressures that in previous years led to health and safety problems at Foxconn Technology, Apple's biggest contract supplier in China.
"Considering the sudden deaths of five people and the similar reason of the deaths, we believe there should be some relations between the tragedy and the working conditions in the factory," said Li Qiang, who runs China Labor Watch.
Apple declined to comment on Tuesday on the deaths at Pegatron. But the company has gone to great lengths in the last few years to improve conditions at the manufacturing facilities that produce Apple products in China. It has stepped up audits, insisted on new safety measures, and supported higher wages and tighter restrictions on working hours.
Apple has even diversified its mix of suppliers with companies like Pegatron, which helps assemble Apple's iPhones and iPads in China, according to people familiar with its operations.
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While Pegatron says it strictly forbids its factories from hiring workers under 16, the legal working age in China, Mr. Shi was able to work using a falsified identity card. In his only month at Pegatron, he worked nearly 280 hours, often 12 hours a day, six days a week, according to work documents his family kept.
Apple's supplier responsibility statement bars employees of supplier companies in China from working more than 60 hours a week; so does Chinese law. But Mr. Shi worked 79 hours in his first week, 77 in his second and 75 in his third, all apparently in violation of the law, according to documents provided by his family.
Pegatron said that the work logs the family kept are records of when the young man clocked in and out, and may not include breaks. The company said his hours did not exceed the legal limit.
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"This is not related to the workplace environment," Ming Tsai, a Pegatron spokeswoman, said Tuesday, referring to the young man's death.
In late July, China Labor Watch released a report claiming that Pegatron was violating Chinese laws and Apple's own social responsibility code of conduct. Among other things, the group said that Pegatron was forcing employees to work unpaid overtime.
Executives at Pegatron, which has 100,000 workers in Shanghai, said they were taking the accusations seriously.
The company spokeswoman said that Pegatron was deeply distraught by the deaths of the workers but that an investigation of the working conditions in the Shanghai factory found nothing unusual, no toxic chemicals or other hazards.
The company tried to resolve the case of Shi Zhaokun by paying his family compensation of about 90,000 renminbi, or about $15,000, according to Shi Zhaokun's uncle, Yang Sen.
But on Tuesday, Mr. Yang insisted the matter was still not resolved. He said something must have gone wrong at the Pegatron workplace. On Sept. 4, he said, his nephew passed a pre-employment physical and was declared healthy.