OTTAWA — Workers at a General Motors assembly plant in Ontario went on strike late Sunday as union leaders reported an impasse in talks to keep Canadian jobs from moving to Mexico.

It is the first strike at a Canadian auto assembly plant in 21 years. The roughly 2,750 unionized employees at the factory, in Ingersoll, Ontario, may have been emboldened because it builds the Chevrolet Equinox, a small sport-utility vehicle that is a sales success for G.M.

A union statement said negotiations had fallen apart over demands that Ingersoll be designated the primary assembly site for the Equinox. In July, production of the GMC Terrain, a similar vehicle, was moved to Mexico from Ingersoll, leading to the loss of 600 jobs at the Canadian factory. The Equinox is also made in Mexico.

“These workers are standing up for good jobs. Not just for themselves, but for the entire community,” said Jerry Dias, president of Unifor, the union representing the workers.