(Adds inventory numbers and recasts lead paragraph)
Sept 18 (Reuters) - Canada's Unifor union said its members at General Motors Co's CAMI auto assembly plant in Ingersoll, Ontario, went on strike as of late Sunday evening after talks on a tentative agreement with the automaker failed.
The union was in talks with GM about the company's decision to cut jobs and shift some production work to Mexico.
In July, GM stopped production of its Terrain sport utility vehicle in Ingersoll, and 100 percent of the volume was moved to Mexico, resulting in 600 layoffs.
A central priority for the union is a commitment from the company to designate the CAMI plant as the lead producer of the Chevrolet Equinox, Unifor said in a statement.
The plant now only produces the Equinox, which is also manufactured in Mexico.
As of Sept 1, GM only had enough inventory of the Equinox model to last 53 days, a rather tight level of supply for the automaker. But with production of the model in Mexico, GM is better placed to withstand the impact of a strike.
The union had blamed the North American Free Trade Agreement (NAFTA) and Mexico's cheaper labor costs for the job losses, which it called unjustified given strong sales of the Equinox crossover and Terrain assembled at the southern Ontario plant.
"Every member understands the importance of reaching a deal that secures production, and what that means to our families and the community," said Mike Van Boekel, Local 88 Chair at the CAMI plant.
Securing jobs was the key to a collective agreement to replace one expiring in September between GM and its 2,800 CAMI workers, said Unifor president Jerry Dias in February.
General Motors said it was disappointed that it was not able to complete a new agreement.
"We encourage Unifor to resume negotiations and to continue working together to secure a competitive agreement," GM Canada said in a statement.
(Reporting by Nick Carey in Detroit, Shubham Kalia and Subrat Patnaik in Bengaluru; Editing by Gopakumar Warrier and Nick Zieminski)