UAW-represented Aramark maintenance employees walked off the job at midnight Saturday at five GM plants.
More than 850 workers went on strike at plants in Michigan and Ohio. The UAW says Aramark employees have been working on an extended contract since March 2018.
According to a UAW news release, key issues involve wages, caps on health insurance, vacation time and retirement.
GM said in a statement that there are "contingency plans in place to cover any potential disruptions."