Unifor national president Jerry Dias says he is appalled with the silence of the federal and provincial governments on the impending closure of the General Motors assembly plant in Oshawa at the end of this year.

"Our governments need to stand up and fight. I'm frankly disgusted by the silence of our governments," Dias told reporters in Windsor, Ont. on Tuesday.

"People need government when they are in trouble. Well, our backs are against the wall and we expect our governments to work with us and fight with us, not to cower in the background and say somehow it's inevitable."

His comments came after he met with representatives of GM at the automaker's headquarters in Detroit on Tuesday afternoon to discuss the fate of the assembly plant.

GM made it clear at the meeting that it is proceeding with the closure. The automaker rejected union proposals to keep the plant open past 2019. The plant, about 60 kilometres east of Toronto, employs more than 2,500 hourly workers.

"I am deeply disappointed at the response from the corporation," Dias said. "What is equally as disappointing is there was a clear acknowledgement that a solution could be found."

Workers of Oshawa's General Motors car assembly plant, listen to Jerry Dias, Unifor national president, the union representing the workers, at the union headquarters in Oshawa. (Eduardo Lima/Canadian Press)

Dias said the fight to keep the Oshawa plant open is not over.

"We are not accepting the closure of our Oshawa facilities under any circumstance," Dias said.

"There was also an acknowledgement that the running of the existing programs, frankly, wouldn't hurt General Motors' bottom line. It may not be profitable, but it certainly wouldn't cause them any sort of deep economic harm. So the choice today was about whether or not we found a solution in the short term to buy us time for a much longer term solution."

GM didn't expect 'backlash' from Canadians

Dias said Unifor will continue its social and print media campaign to persuade GM to keep the plant operating. That means it is exploring all legal options and may launch a challenge over a possible violation of its collective agreement with GM, signed in 2016.

Unifor will also hold a "major" rally in Windsor on Friday. The union expects thousands of people to attend and Dias said the rally is "but a mere start" of the union's campaign.

Dias said he is not advocating a boycott of GM products, but said Canadian and American workers and consumers are furious with the automaker's decision to shut down the Oshawa assembly plant.

"I'm convinced that General Motors didn't expect the backlash that they're facing from Canadians, but faced with all of the facts that have unfolded over the last six weeks since their announcement, in my opinion, they haven't reached far enough or deep enough to find a solution."

General Motors will close its production plant in Oshawa at the end of the year. (Eduardo Lima/Canadian Press)

GM announced in November that work at the plant would end by December 2019, a decision that Unifor has forcefully challenged. The union has criticized GM for moving jobs to Mexico and it released a scathing attack ad ahead of the meeting.

GM says proposals do not 'address the economic situation'

In a statement released ahead of Dias's news conference, GM said it is standing firm on its decision to close the plant.

David Paterson, vice president of corporate affairs at GM Canada, said in a phone interview that the options suggested by the union, including extending the life of the Chevy Impala and Cadillac XTS currently produced at the plant ,or shifting production slated for Mexico to the plant, are not economically sound.

"We studied all of the different proposals in detail, some of which we studied in detail before, and they all added substantial incremental cost and they would not address the economic situation that we have with the shift in the marketplace."

Paterson said the move in the auto market away from cars means the company has to transition away from the models built in Oshawa. He said it is too expensive and will take too long to shift other production to the already under capacity Oshawa plant.

He said the union should instead work with the company on timing and transition plans for the close to 3,000 jobs affected by the closure. 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 workers gather for a meeting at UNIFOR Local 222 near the General Motors assembly plant in Oshawa, Ont. (Carlos Osorio/Reuters)

The company also said about half of more than 2,500 hourly workers employed at the plant are eligible for a pension. Retirement benefits include about $3,500 a month, a $20,000 car voucher, and a lump sum payment of about $50,000, said Paterson.

GM has 'picked a fight with all of Canada'

At the news conference, Dias said GM's decision will affect more than just Oshawa.

"GM today, by reconfirming their decision, has not only picked a fight frankly with Unifor, but they have picked a fight with all of Canada," Dias said.

"This is about corporate greed."

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 also emphasized that the closure will affect many spin-off jobs that depend on the Oshawa plant.

Workers at the plant, according to Unifor, staged a sit-down protest against the closure on Tuesday night.

Hey <a href="https://twitter.com/GM?ref_src=twsrc%5Etfw">@GM</a> if you want to sell in Canada, you need to keep building in <a href="https://twitter.com/hashtag/Oshawa?src=hash&ref_src=twsrc%5Etfw">#Oshawa</a> say workers who are peacefully protesting tonight, sitting at their benches at the plant <a href="https://twitter.com/GMcanada?ref_src=twsrc%5Etfw">@GMcanada</a> plans to close. <a href="https://twitter.com/hashtag/SaveOshawaGM?src=hash&ref_src=twsrc%5Etfw">#SaveOshawaGM</a> <a href="https://twitter.com/hashtag/canlab?src=hash&ref_src=twsrc%5Etfw">#canlab</a> <a href="https://twitter.com/mtbarra?ref_src=twsrc%5Etfw">@mtbarra</a> <a href="https://t.co/5HYIDMgpTC">pic.twitter.com/5HYIDMgpTC</a> —@UniforTheUnion

The company said it will close five plants, four of which are in the United States. The Oshawa plant first opened in 1918.