This latest incident followed tighter rules to prevent tiny indentations on the phones and scratches to the phones' frames and back covers. The new iPhone 5 is said to be more susceptible to such markings.

A worker at the plant told IDG News Service Friday that because quality controls have been stepped up, more products are being intercepted before they leave the production line, which means volume targets aren't being met.

"As a result, there was conflict and they beat our people," said the worker, who did not give her name but said she works in the "quality department."

She claimed workers at the plant were beaten twice last week for similar reasons. "Our long-suppressed anger erupted and we went on strike," she said, communicating via Tencent Weibo, a Chinese Twitter-like service.