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(AP) — The United Auto Workers union has once again escalated its strikes against big Detroit automakers, this time adding a factory that makes Ram pickup trucks for Stellantis.

The union said that 6,800 members walked out Monday morning and shut down the Sterling Heights, Michigan, Assembly Plant, a huge profit center for the company.

The newest strike action comes just three days after union President Shawn Fain reported progress in talks with General Motors and Stellantis but said the companies will have to make better offers. No progress was reported with Ford, which last week said it had the best offer of the three.

The union went on strike Sept. 15 at one assembly plant from each company. About 40,800 workers are now on strike against all three automakers. The strikes, now in their sixth week, cover seven assembly plants and 38 parts warehouses.

In its statement, the union said that offers from Stellantis, formed in the 2021 merger of Fiat Chrysler and France’s PSA Groupe, lag Ford and GM despite the automaker having the most revenue and highest profits of the three.

Stellantis has the worst offer on cost of living raises, how fast workers move to the top of the pay scale, temporary worker pay, converting temps to full time, and other issues, the union said.