The weekslong United Auto Workers strike intensified Monday when 6,800 employees at Stellantis walked off the job at the automaker’s largest plant in Sterling Heights, Michigan.

Stellantis’ Sterling Heights Assembly Plant produces the Ram 1500 trucks, one of the company’s best-selling vehicles, UAW leaders said Monday. With another 6,800 in the fold, the UAW now has more than 40,000 workers on strike. 

Stellantis (the parent company of Chrysler, Dodge, Jeep and Ram) didn’t immediately respond to a request for comment. In a statement last Friday, Stellantis officials said UAW negotiations “continue to be productive” but their focus is on “finding solutions that protect the company and our employees.”

UAW leaders also said Monday that Stellantis has the weakest contract offer on the table among Detroit’s Big Three automakers. Each automaker has proposed a 23% wage increase across a four-year contract but there are some key differences in Stellantis’ offer, the union said. 

Despite having generated the highest revenue, profits and cash reserves among the Big Three, according to the union, Stellantis has failed to meet union demands with its latest offer — specifically on temporary worker pay, cost-of-living adjustments and other areas.

Stellantis hasn’t published its latest contract offer, but according to the union’s tally, the most recent proposal doesn’t offer profit-sharing pay to temporary workers and the cost-of-living adjustment doesn’t take effect in the first year of the contract. Under the latest Stellantis proposal, it would also take employees four years to reach the top pay rate while Ford and GM’s proposal offers top pay rates in three years, according to the UAW. 

UAW leaders and the automakers have spent weeks trying to produce a new, four-year labor contract. However, the Stellantis strike suggests that union leadership and company officials are not close to reaching an agreement. 

The Big Three “made a combined $21 billion in total profits in just the first six months of this year and yet all of them are still refusing to settle contracts that give workers a fair share of the record profits they’ve earned,” the UAW said in a statement Monday. 

Organized labor experts noted that the Sterling Heights walkout marks the second time the UAW has made a surprise strike on one of the automakers — the first being earlier this month when 8,700 UAW members walked out of a Ford plant in Kentucky. “That pressure will continue to escalate unless the automakers, particularly Stellantis, make greater concessions,” said Lynne Vincent, a business management professor at Syracuse University who studies the psychological impacts of strikes.

“The latest move is consistent with the UAW’s unfolding strategy, which is to not play by the traditional playbook, escalate as needed, and be nimble,” Vincent told CBS MoneyWatch. “The strategy is to be unpredictable in that the UAW’s plans are not communicated ahead of time.”

The UAW strike began last month when thousands of workers left their post when the contract between workers and the automakers expired on September 14. Since then, the automakers have laid off thousands of employees and blamed their moves on the prolonged work stoppage. 

The strike so far has caused $9.3 billion in losses for the U.S. auto industry, according to the Anderson Economic Group. That includes $488 million in wages lost for striking autoworkers and $4.18 billion losses for the Big Three. 

“This is a tough strike for the automakers and the workers,” Vincent said. “The longer the duration of the strike, the tougher it is for all involved.”  

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