THE United Auto Workers (UAW) union widened its strike against General Motors on Sunday, the last of the “Big Three” Detroit car makers who have as yet failed to come to a contract agreement with the union.

Car workers in Canada have walked out all Stellantis plants over the company’s failure to agree a new contract.

UAW agreed tentative deals with Ford and Stellantis in the last week, which now need to be approved by union members. But General Motors is holding out and so far is refusing to match the deal agreed with its main competitors.

Union members walked out at the Spring Hill Manufacturers’ plant in Tennessee, GM’s largest site in North America, just hours after the Stellantis deal was reached.

Some 4,000 workers joined 14,000 GM workers already striking at GM factories in Texas, Michigan and Missouri.

GM said in a statement that it was disappointed with the expanded strike “in light of the progress we have made,” saying that it has bargained in good faith and wants a deal as soon as possible.

UAW president Shawn Fain said: “We are disappointed by GM’s unnecessary and irresponsible refusal to come to a fair agreement.”

The main sticking point in the negotiations are reportedly retirement benefits and the ending of temporary workers status. 

GM has more retired workers than Ford or Stellantis and increases to pension benefits for workers hired before 2007 are said to cost GM more than its rivals.

The continued impasse at GM comes as more than 8,200 members of Canadian union Unifor walked out at all Stellantis plants across the country after new contract talks stalled.

The union said in a statement: “We have made progress and we will continue to negotiate.” 

Stellantis said that it was “extremely disappointed” with the strike action but would continue to bargain until an agreement is reached.