You didn't see it on TV if you live in the U.S., but the labor union representing autoworkers in Canada aired a Super Bowl ad lambasting General Motors over its plans to close a plant in Oshawa , Ontario, despite threats of a lawsuit from the automaker.The 30-second spot is titled " GM Leaves Canadians Out in the Cold," and it's part of calls to boycott Mexican-built GM vehicles in a bid to save the Oshawa plant, which builds the Cadillac XTS Chevrolet Impala and Silverado pickup, and GMC Sierra . It aired on Canadian TV stations during the Super Bowl on Sunday.GM in November announced plans to end production at five assembly plants including Oshawa, which is near Toronto, leaving 2,600 blue-collar workers facing the prospect of losing their jobs by the end of the year. Both Unifor and the UAW have criticized GM for building too many products in Mexico, including the new Chevrolet Blazer , to be sold in Canada and the U.S. The Oshawa plant formerly built the Chevy Equinox until GM fully moved production of the crossover to Mexico in 2017.The ad asserts that GM benefited from a nearly $11 billion bailout from the Canadian government, the equivalent, it says, of $300 from every Canadian. It says the decision to expand in Mexico is "as un-Canadian as the vehicles they now want to sell us." It closes by saying, "GM, you may have forgotten our generosity, but we'll never forget your greed."Last week, a law firm representing General Motors of Canada Co., wrote to Unifor President Jerry Dias urging the union to cease "any and all further publication" of the ad. It alleges the ad contains false and misleading claims about the federal bailout at issue. GM on Sunday issued a statement saying the ad is misleading."Unifor knows that GM Canada repaid its 2009 loans in full, and that the restructured GM fulfilled all the terms of its agreements with the Canadian government many years ago," the company said. "Since 2009, GM Canada has contributed over $100 billion to the Canadian economy including $8 billion invested into worker pensions."The cease-and-desist letter gave a Saturday deadline to stop airing the ad, but Unifor continues to show the ad. On YouTube , it had racked up more than 80,000 views as of Monday morning since being posted Jan. 21."We stand by the belief that if GM wants to sell here, then it needs to build here, and we will not be intimidated from sharing that message with Canadians in this ad," Dias said in a statement.