DETROIT (AP) — About 2,500 workers at a Canadian General Motors plant that makes the Chevrolet Equinox SUV are on strike in a dispute over job security.

Members of Unifor Local 88 in Ingersoll, Ontario, west of Toronto, stopped working when their contract expired at 10:59 p.m. Sunday.

The strike couldn't come at worse time for GM. A new version of the Equinox compact SUV just started to hit dealerships during the summer, attracting buyers in the hottest part of the U.S. auto market.

The union says GM won't designate the factory as lead producer of the Equinox. GM moved production of the GMC Terrain, which is similar to the Equinox, to Mexico in July, and 600 workers were laid off. The Equinox also is made in Mexico and workers fear more jobs could go south.

GM says in a statement that it encourages the union to resume negotiations. The company says both sides made positive progress during the past several weeks.

Equinox sales in the U.S. are up 17 percent through August to more than 185,000.

GM says the Ingersoll plant is operating at maximum capacity on three shifts, and with the compact SUV market continuing to grow, it will need another factory to handle future demand. The company said that in 2015 it invested 800 million Canadian dollars ($656 million U.S.) in the plant to build the new Equinox.

The contract at the Ingersoll plant is negotiated separately from Unifor's main contract with the auto industry.

The Ingersoll plant started as a joint venture between GM and Suzuki, and GM now owns the entire factory.