Nearly 4,300 Canadian autoworkers employed by General Motors went on strike Tuesday morning after negotiations flatlined on Monday night.

The walkout came after Unifor, Canada’s largest private sector labor union, said that GM was “stubbornly refusing” to match the labor agreement that Ford Motor Co. had agreed to last month. Ford’s contract provided wage hikes of up to 25% for the automaker’s 5,600 workers in Canada represented by Unifor.

Although Unifor’s labor contracts with the Detroit Three Automakers were set to expire on Sept. 18, the union delayed negotiations with GM and Stellantis in order to finish bargaining with Ford. The Canadian union is relying on pattern bargaining, or using one agreement as a benchmark for other contracts, to force GM to match Ford’s contract.

The union’s president, Lara Payne, said Monday that GM continues to fall short of meeting Unifor’s demands related to pensions, income support for retirees and “meaningful steps” to transition temporary workers into full-timers.

“This strike is about General Motors stubbornly refusing to meet the pattern agreement. The company knows our members will never let GM break our pattern – not today – not ever,” Payne said.

The striking workers are employed at GM’s Oshawa Assembly Complex — which makes light- and heavy-duty Chevrolet Silverado trucks — and St. Catharines Powertrain Plant, which produces engines for vehicles such as the Chevrolet Equinox and Corvette. The automaker’s Woodstock parts distribution center is also struck.

Roughly 9,200 members of the United Auto Workers union in the U.S. are currently on strike against the company’s 20 parts distribution centers, as well as GM’s Lansing Delta Township assembly plant and Wentzville, Missouri, assembly complex. Some 25,000 autoworkers are striking against the Detroit Three’s facilities across the U.S.

In a statement, GM said Tuesday that the company is committed to working with Unifor to reach an agreement that is “fair and flexible” for its employees.