TORONTO—General Motors Co. plans to lay off up to 600 workers at a southwestern Ontario plant as production for its older Chevrolet Equinox sport-utility vehicle winds down and production of a new SUV model is being moved in Mexico.

Unifor Local 88 President Dan Borthwick said Friday that GM informed him it will end older Equinox production at its CAMI Assembly plant in Ingersoll, Ontario, nearly 100 miles east of Toronto, in July, about a year earlier than scheduled.

...