The union representing workers at General Motors' Oshawa assembly plant on Friday called on Canadians to boycott any of the automaker's vehicles manufactured in Mexico.

Unifor national president Jerry Dias said the union has done "everything possible" to avoid a boycott but their efforts have fell on deaf ears at the multinational auto giant.

"We need to remind [GM management] that we are not going to forgive them for walking away from us," Dias told reporters in downtown Toronto.

"So as GM has choices, Canadian and American consumers have choices."

Last November, GM announced it would close the sprawling Oshawa plant in December this year, putting some 2,500 employees out of work. The move was part of a global restructuring that also included the closure of four U.S. facilities.

"General Motors is arrogant to the point that they think that they can close our assembly plant in Oshawa, that they can close four plants in the U.S., while ramping up production in Mexico," Dias said, adding that the boycott is not supposed to be an attack on Mexican workers.

The ultimate purpose of the boycott is to pressure GM to keep the Oshawa plant open until December 2020. During negotiations of the last collective agreement in 2016, GM management said that there would be no closures in Canada during the duration of the deal, according to Dias.

"Their word must mean something," he said.

Dias said that polling commissioned by Unifor has suggested widespread public support for a boycott. The campaign will include ads on television, in the media and on billboards in both Canada and the U.S.