WINDSOR, Ont. -- General Motors is sticking with its plans to shut the Oshawa Assembly Plant by the end of the year in a move the head of Unifor says is motivated by "corporate greed."

Unifor president Jerry Dias sat down with GM Tuesday to talk about the proposals the union had made to extend the life of the Ontario plant but came away empty-handed.

"I am deeply disappointed by the response from the corporation," said Dias at a press conference in Windsor, Ont.

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 economic, said David Paterson, vice president of corporate affairs at GM Canada.

"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 in a phone interview that the move in the auto market away from cars means the company has to transition away from the models, while 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 impacted. 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.

The company also said about half of the 2,600 hourly workers 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.

Dias said he's not accepting the end of Oshawa, and that the company acknowledged in the meeting it would be possible to extend current production at the plant.

"It may not be profitable, but it certainly wouldn't cause them any sort of deep economic harm," said Dais.

"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," he said.

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 the many spin-off jobs that depend on the Oshawa plant and the wider impacts of its closure on the economy.

"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," said Dias.