Toronto - There's a big tussle brewing between General Motors and a Canadian motor industry workers union after the latter aired a commercial during the Super Bowl that blatantly mocked the US carmaker.

The 30-second ad, which calls General Motors greedy and "un-Canadian", broadcast on Canadian TV stations during Sunday's game.

This follows GM's announcement in November last year that it plans to close its car factory in Oshawa, Ontario, near Toronto, which will put around 2600 blue-collar employees out of work.

The ad accuses GM of continuing to expand in Mexico while leaving Canadians "out in the cold" and also drags up the company's 2009 bail out, claiming that the carmaker received the equivalent of $300 from every Canadian.

GM of Canada previously sent a cease-and-desist letter to the Unifor union, giving it a Saturday deadline to stop using the ad, but the demand wasn't heeded. GM said in a statement that the ad is misleading and inaccurate, and is now threatening to sue the union, according to the Detroit Free Press.

Unifor President Jerry Dias is not backing down for anything, however: “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.”