By Ethan Lou

TORONTO (Reuters) - Canada's Unifor union has set a tentative strike deadline of midnight Oct. 10 for talks with Fiat Chrysler Automobiles NV <FCHA.MI>, the labor group said on Saturday as it prepares to vote on a related deal with General Motors Co <GM.N>.

Unifor, which represents close to 10,000 Fiat Chrysler workers in Canada, said in a statement the strike deadline of 11:59 p.m. will stand if talks with Fiat Chrysler begin "immediately" after the union ratifies its contract with General Motors Co <GM.N> on Sunday.

A four-year contract covering roughly 20,000 Canadian unionized workers of Fiat Chrysler, GM and Ford Motor Co <F.N> expired on Sept. 19. Unifor, which represents some 4,000 GM workers, reached a last-minute tentative deal with the company late on that day.

Under a process called patterned bargaining, Unifor's tentative agreement with GM, if ratified by members, would be used as a template for talks with the other companies, which are expected to agree to similar terms.

"Should the tentative agreement not be approved by the membership ... the union will move towards an immediate strike position," union spokeswoman Denise Hammond said.

Unifor's deal with GM granted some job security, but less favorable pensions than before. The company agreed to renewed investment at its Canadian plants, while the union gave up defined benefits pensions for new hires.

Unifor President Jerry Dias has said concessions were necessary to ensure GM continues operations in the province of Ontario, home to nearly all of Canada's once-thriving auto industry that has been losing out to the Southern United States and lower-cost Mexico.

Under the new deal, GM's plant in Oshawa, just east of Toronto, will eventually perform final assembly work on at least 70,000 Silverado pickup trucks a year, according to two sources close to negotiations.

Sales of the truck have been strong amid a recovery in the U.S. housing market and stable fuel prices. Analysts and company executives have said it is among the most profitable vehicles for Detroit automakers.

GM's St. Catharines plant in southern Ontario will have new work in the form of engine production, moved from Mexico, according to Unifor.

The union had agreed to a pure defined contribution pension plan for new hires, which unlike the plan held by current workers does not guarantee a set payout.

For Fiat Chrysler, Unifor has said it seeks terms including an upgrade to an outdated paint shop at a plant in Brampton, west of Toronto.

(Editing by Matthew Lewis)