GM stunned the North American auto industry in late November when it announced a major restructuring plan that will see up to 14,000 workers in North America lose their jobs, almost 3,000 of which are in the Oshawa Assembly Plant.
After he returned from the meeting with GM, Dias told reporters in a press conference in Windsor, Ontario, that the union was looking at its legal options regarding whether the Detroit company violated the labor contract.
"Workers on the morning shift at Oshawa Assembly Plant staged a sit down to protest General Motors callous choice to close down the plant after 100 years of operation, despite the fact that the company acknowledges it could maintain the plant without injury to its current bottom line", Unifor spokesperson Kathleen O'Keefe said in an email.
There has been no word on if the sit-in will evolve into a complete walk-out. "GM today has not only picked a fight with Unifor, but picked a fight with all of Canada".
Production at the Oshawa plant began on November 7, 1953, and in the 1980s the plant employed roughly 23,000 people.
GM said in a letter to Dias that it had already considered several proposals including those the union raised at the meeting.
A large rally has also been planned by the union for 10:30 a.m.in Windsor on Friday - scheduled to coincide with an investors' meeting GM is hosting across the river in Detroit. "We are not going anywhere".
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Dias previously promised "one hell of a fight" to prevent the Oshawa plant's closure.
"We understand our union's frustration but need to now work together to deliver supports, transition and training for our employees for new opportunities over the coming year", spokeswoman Jennifer Wright wrote in an e-mail.
"I'm furious right now", Dias added.
GM has, for its part, has said that the closure of the plant is necessary as it shifts its focus to electric and autonomous vehicles.
Unifor has been running ads critical of the company's decision and highlighting that it accepted $11 billion in bailout funds from Canadian governments in the financial downturn.
The union has emphasized the wider economic impacts of the shutdown and released a study Wednesday putting some hard numbers to the claims.
GM executives met with Jerry Dias, president of the union representing about 2,500 Oshawa auto workers on Tuesday, to discuss the proposals brought forward by Unifor in December that would keep the Oshawa facility open past 2019.