Even so, Foxconn's Chinese plants have had problems before. Last month, 2000 workers in Taiyuan after what workers described as aggressive behavior from security guards.

In spite of Foxconn's claims that everything is just fine, the company has been cracking down on workers to prevent tiny indentations on the iPhone 5--the anodized aluminum on its back and edges is , especially on the black model.

China Labor Watch had claimed that a fight between workers and quality-control inspectors resulted in some injuries that sent some people to go to the hospital.

"They have such high expectations for these products, even if you raise the demands a little bit it makes a huge difference to the pressure on the workers," says Li Qiang, China Labor Watch's executive director, in an interview.