Unable to sway General Motors Corp. from shuttering a truck plant in Ontario, Canadian Auto Workers continue to protest outside the auto maker’s regional headquarters in Oshawa and ponder more aggressive action.

CAW President Buzz Hargrove met with GM Chairman and CEO Rick Wagoner earlier today with hopes of halting the auto maker’s plan to idle Oshawa, one of four truck plants it will close in North America due to a market shift toward passenger cars in the face of high gasoline prices.

CAW spokeswoman Shannon Devine confirms Hargrove and the CAW Local 222 leadership met with Wagoner and other top GM brass this morning. Hargrove told Wagoner the decision violates terms of a recent labor agreement with the union, Devine says, but GM would not relent.

Hargrove now promises to consider his options, which could include a strike at a GM plant, arbitration or intervention by Canada’s labor board, according to media reports.

GM announced earlier this week it would close Oshawa, as well as SUV plants in Moraine, OH; Janesville, WI; and Toluca, Mexico. Oshawa will close in 2009 and Janesville and Moraine will follow by the end of 2010. The Mexican plant, which builds medium-duty Chevrolet Kodiak pickups, will start the cadence at the end of this year.

The production cuts will trim GM’s high-profit truck output in the North America by 700,000 units in 2010, bringing its overall production in the region to 3.7 million units annually. It plans to add third shifts at passenger car plants in Michigan and Ohio.

The plant closures and production changes come in response to a shift in consumer demand that threatens to jeopardize the auto maker’s turnaround plan.

“Higher gas prices are changing consumer behavior and rapidly, significantly affecting the U.S. auto industry sales mix,” Wagoner told journalists prior to the company’s annual meeting in Wilmington, DE, on Tuesday.

GM’s refusal to budge on Oshawa’s future comes ahead of a CAW collective-bargaining and political-action meeting in Toronto on Monday. Nearly 1,000 elected delegates and guests from across Canada will discuss and debate the CAW’s agenda for the next three years.