"Unfortunately, all Unifor's proposals would involve substantial incremental costs and a further deterioration of GM's competitive position", GM said, adding that "it can not pursue them" because of the weakening market in North America.
The action came after Unifor, the union representing the autoworkers, failed to win GM's support for its proposals to save the plant.
Dias said the US$22-million annual salary of company CEO Mary Barra is greater than the entire payroll of one assembly plant in Mexico.
Meanwhile Dias says of the closure "There would be a major ripple effect that would be felt far beyond Oshawa and even Ontario.We're asking Canadians and governments at all levels to make it clear to GM that we will hold them accountable should they decide to inflict this damage by closing a top-quality and productive plant for no other reason than corporate greed".
An angry Dias spoke to media in Windsor after Tuesday's meeting.
When asked if the union would consider litigation against the company like the United Auto Workers in the U.S., Dias said they are considering their legal options. He added how the Canadian governments and taxpayers also provided $11 billion in subsidies to GM at a time when it faced near bankruptcy a decade ago.
GM confirmed it has no plans to build vehicles in the Oshawa plant after the end of 2019, which is part of a broad restructuring announced in November.
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David Paterson, vice president of corporate affairs at GM Canada, said the union should instead work with the company on timing and transition plans for the workers who are losing their jobs.
Dias said the union is still not be accepting the closure of our Oshawa facilities. GM said it has identified job opportunities, is willing to pay for retraining, and is open to negotiations on packages for workers on top of what is already included in contracts.
GM officials have said the fate of the US plants is subject to talks with the United Auto Workers union, which represents the USA workers at those plants.
On Tuesday night, truck assembly stopped completely for almost five hours, Unifor said.
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.
With the GM world headquarters towers looming in the Detroit background, a billboard message from Unifor on Wyandotte Street East in Windsor, shown January 8, 2019, has a message about the automaker's Oshawa Assembly Plant.
GM workers responded by walking off the job.