A GM spokesman declined to comment further on the move.
Efforts to seek comment from the UAW in Lansing and at its international headquarters in Detroit were unsuccessful.
The production shift is expected to happen in 2015, and would be for the 2015 or 2016 model year. GM sold 78,554 Camaros in the United States through November, down 4 percent from the same 11 months of 2011, according to the Automotive News Data Center.
GM told the Canadian Auto Workers that the decision was made two weeks ago, so the move wasn't influenced by Michigan's new right-to-work law that passed last week, CAW President Ken Lewenza said during a conference call this afternoon.
Lewenza, who described the decision an "assault on Canada," said the plant produces 100,000 Camaros annually, which accounts for around 25-30 percent of the plant's total output.
"When you take 25 to 30 percent production out of a facility, without a commitment to replace it, that means 25 to 30 percent of our existing membership can lose their jobs as a result of this decision. It's simple mathematics."
It was not clear how many jobs could be lost.
Lewenza said the union was caught off guard by the decision. The union, he said, made significant sacrifices to win the Camaro work in 2006.
"Needless to say, it was the home of the revitalization of the Camaro," Lewenza said.
During contract negotiations this fall, the union said GM misled them by telling them the next generation Camaro hadn't even been approved yet. The CAW called on GM to replace production at the plant on a one-to-one basis.
Toronto's Globe and Mail and Reuters reported the story earlier today.
The Globe and Mail also reported that GM's agreement with the CAW in September said GM would continue to build the Camaro in Oshawa until the end of the current generation but made no promises about future generations.
A third shift is being added to the Oshawa plant in early 2013 to assemble the next generation of the Chevrolet Impala, GM said.