Sterling Heights, Michigan - The United Auto Workers union has halted work at a giant Stellantis truck plant on Monday, expanding a five-week strike hitting Detroit automakers.

The latest UAW move means that 6,800 workers will walk off the job in Sterling Heights, Michigan, where the European auto giant assembles the highly profitable Ram 1500 pickup trucks.

On Friday, UAW President Shawn Fain reported progress in talks with Stellantis, but said further concessions were possible and necessary for a deal that would end the stoppage.

The union on September 15 ordered a strike of Stellantis and fellow Big Three automakers General Motors and Ford with a stoppage of just three plants with about 12,700 UAW members.

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The union has kept up the pressure by expanding the strike to additional factories.

With Monday's action, the number of UAW workers on strike now stands at more than 40,000, according to a UAW press release.

"Despite having the highest revenue, the highest profits (North American and global), the highest profit margins, and the most cash in reserve, Stellantis lags behind both Ford and General Motors in addressing the demands of their UAW workforce," the UAW said.

"Currently, Stellantis has the worst proposal on the table regarding wage progression, temporary worker pay and conversion to full-time, cost-of-living adjustments (COLA), and more."