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STORY: U.S. automakers this week are expected to show a rise in sales in the third quarter.

General Motors was set to remain the top-selling automaker, with Toyota ranking second, according to

car shopping website Edmunds.

But ongoing labor strikes at GM, Ford and Chrysler-parent Stellantis could muddy the outlook for the rest of the year.

Launched last month, the United Auto Workers’ union initially targeted one assembly plant at each of the Detroit Three. The strike was later expanded to other plants as talks failed to progress.

S&P forecast daily losses from the strike at the three plants at over 4,000 vehicles, warning further walkouts may lead to cumulative losses reaching hundreds of thousands of autos.

Meanwhile, GM and Ford on Monday said they are laying off another 500 workers at four Midwestern plants, part of the ripple effect of the strikes. The Detroit Three have already laid off some 3,000 workers combined, many at plants that supply parts.

The automakers haven't disclosed a financial hit from the strikes so far, but JPMorgan in a research note on Monday estimated the work stoppages have cost GM $191 million and Ford $145 million.

The UAW said it presented a new contract offer to GM on Monday. GM received the counterproposal, but said “significant gaps remain." The union also held a new round of bargaining with Stellantis.