Members of Unifor have gone on strike against General Motors Co. at the company's assembly plant in Ingersoll, Ont., a move that cuts off the main supply of the auto maker's hot-selling Chevrolet Equinox vehicles.

Negotiators for the auto maker and Unifor, the union that represents about 2,800 workers at Cami Automotive, were unable to reach a deal on a new contract before a 10:59 p.m. EDT Sunday deadline.

A shutdown of the plant will have had a ripple effect through GM's other operations, including an engine and transmission plant in St. Catharines, Ont., that supplies Cami, as well as leading to a halt in production at other suppliers that make seats and other components.

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The union was seeking a formal commitment from GM that Equinox production would remain at Cami and that it would be anointed as the lead plant for the vehicle. That designation means it would be first plant to receive the hundreds of millions of dollars in new investment required when a vehicle is redesigned.

GM officials refused to designate Cami as the lead plant for future Equinox production, union sources said, and offered investment of $60-million, compared to $400-million earmarked for a plant in Oshawa, Ont., during contract talks last year.

"We have to protect the Equinox," a senior union official said Sunday as negotiations went down to the wire.

GM spent about $500-million to retool Cami for a new version of the Equinox for the 2017 model year, but the crossover is also assembled in small numbers at two plants in Mexico.

The issue of Mexico was pivotal in the talks, because GM announced earlier this year that it would shift production of the GMC version of the compact crossover, the Terrain, to Mexico. Terrain production ended at Cami this summer and eliminated 600 jobs.

The Equinox has been such a key vehicle for GM that Cami has been running three shifts, six days a week, for several years, making it one of the most productive and profitable assembly plants in GM's North American operations.

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North American drivers are increasingly switching to compact crossovers and other utility vehicles from sedans and other passenger cars.

Workers assembled more than 300,000 vehicles at Cami last year.

Cami began production in 1989 as a joint venture between GM and Suzuki Motor Co. Ltd., but GM bought out its partner during the 2008-2009 financial crisis and Cami stopped assembling Suzuki vehicles.

The Unifor members at Cami work under a different contract than their colleagues at other GM assembly and parts plants in Canada.

The contract Unifor bargained for those workers last year included $12,000 in bonuses over four years and an extension of the life of a vehicle assembly plant in Oshawa that was on the endangered list.

GM agreed to ship unfinished frames of full-sized pickup truck bodies to Oshawa from Fort Wayne, Ind. Workers in Oshawa will perform final assembly of those vehicles, with that work scheduled to begin in November.