More than 4,000 autoworkers in Canada are on strike against General Motors after the Unifor union and the company failed to agree to a deal similar to the one the union previously reached with Ford.

"The company continues to fall short on our pension demands, income supports for retired workers, and meaningful steps to transition temporary workers into permanent, full-time jobs," Unifor said in a statement.

The Canadian plants on strike include an assembly factory in Oshawa, Ontario, one of the factories that builds the Silverado pickup, as well as an engine and transmission plant in St. Catharines, Ontario. Unifor members at GM's CAMI Assembly Plant in Ingersoll, Ontario are covered by a separate collective agreement and will remain on the job.

But the plants that are on strike could affect GM's US operations, because its engines and transmissions are used in vehicles built here. The Silverado is GM's best-selling and one of its most profitable vehicles, so shutting production there will serve a blow to GM's sales and revenue -- even though it still makes the Silverado at two US plants, one in Flint, Michigan, and one in Fort Wayne, Indiana.

GM already is dealing with a strike by the United Auto Workers union at two of its US assembly plants and a strike of 18 parts distribution centers across 20 states. The UAW is also on strike against plants at GM rivals Ford and Stellantis, which builds cars under the Jeep, Ram, Dodge and Chrysler names. GM had already disclosed that it lost $200 million in the first two weeks of the UAW strike, which began on September 15.

But UAW President Shawn Fain announced on Friday that GM had agreed to a key union demand including current and future EV battery plants in its national labor agreement with that union, a move that averted a UAW threat to expand the strike to a key US plant that makes full-size SUVs.

The UAW remained on strike at the GM plants where its members had already walked out. But that announcement raised hopes the company was getting closer to putting its labor problems behind it.