The United Auto Workers union sent 6,800 Stellantis employees to the picket line Monday morning in a surprise, targeted strike at the company's Dodge Ram facility.

The Sterling Heights Assembly Plant is Stellantis' "largest plant and biggest moneymaker," UAW said in a statement Monday. The union said the company, which makes vehicles under the Dodge, Ram, Jeep and Chrysler brands, has "the worst proposal on the table" in its negotiations on pay, converting temporary workers to full time and cost-of-living adjustments.

"Despite having the highest revenue, ... 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.

This is the second "surprise" targeted strike in two weeks by the UAW. The first was at Ford on October 11.

On Friday, Stellantis said, "Negotiations between Stellantis and the UAW continue to be productive, building on the momentum from the past several weeks. We have made progress on narrowing the gaps on significant issues."

CNN has reached out to Stellantis for comment on this expanded strike.

There are now more than 40,000 UAW members on strike as it enters its sixth week. The Big Three automakers have laid off thousands of workers as a result. The first four weeks of the strike has had an economic impact of $7.7 billion, according to Anderson Economic Group.

This is a developing story. It will be updated.