The United Auto Workers union recently began a strike against Ford, GM and Stellantis, marking the first time in the organization’s history that union members walked out on all three companies simultaneously. Workers commenced strike actions at three plants in Missouri, Michigan and Ohio on September 15, according to the Associated Press.

The UAW strikes began at General Motors’ Wentzville, Missouri plant, where 3,600 UAW members are employed. Later, 3,300 workers walked out of Ford’s Wayne, Michigan plant as well as Stellantis’ Toledo, Ohio assembly complex, which employs about 5,800 UAW members.

According to CNN, roughly 13,000 UAW members walked off the job, but not all 146,000 unionized UAW workers have begun striking yet.

“As time goes on, more locals may be called on to ‘Stand Up’ and join the strike,” the union told its members on the UAW website. “This gives us maximum leverage and maximum flexibility in our fight to win a fair contract at each of the Big Three automakers.”

The strikes came after contract negotiations with the three automakers failed to meet the union’s demand for a 36% wage increase over the next four years. GM and Ford only offered a 20% wage hike while Stellantis proposed a 17.5% wage increase.

Jeff Schuster, the head of automotive for the research firm GlobalData, predicted that this strike could last longer than prior work stoppages, which includes the 40-strike against General Motors that took place in 2019. “This one feels like there’s a lot more at risk here on both sides,” he added.