There are usually 3,000 workers onsite at Tianjin Mitsumi Electric Co. factory in the Chinese city of Tianjin. But no work has been done here since Tuesday. Workers at this Japanese-owned electronics factory are on strike.

A sign placed at the factory's entrance gate reads, "We want a pay raise" and "We want fair treatment."

It follows strikes at other foreign-owned factories in China—including factories run by Honda and Toyota—as workers demand higher wages and better conditions.

This spate of factory strikes could become a worry for the ruling Chinese Communist Party, which fears public discontent could erode its authority—and alarm foreign investors.