Workers represented by the United Auto Workers union walked out on strike on two plants operated by Chrysler LLC, while another of the automaker's key assembly plants was told to remain on hold.

Chrysler workers began leaving work sites in Sterling Heights and Warren, Michigan, witnesses and union officials said.

A union official at Chrysler's Belvidere, Illinois assembly plant said he had been told to remain on hold and keep workers at that plant on the job.

Earlier, the UAW's chief negotiator with Chrysler said the union planned a targeted strike that would exempt five plants that had already been idled by the automaker.