More than 2,700 union workers at GM's CAMI Assembly Plant in Ingersoll, Ontario walked off the job early Monday morning.
The plant builds GM's best-selling crossover, the Chevy Equinox. GM also builds the Equinox in Mexico.
Unifor union leaders want GM to designate the Ingersoll plant the lead factory for the Equinox, which would mean a long-term commitment to jobs at the plant.
GM recently ended production of the GMC Terrain at CAMI Assembly, moving hundreds of jobs to Mexico.