Sen. Bernie Sanders addressed autoworkers in Detroit on Friday, calling on working people across the U.S. to stand in solidarity with the walkout.
Sanders called out General Motors CEO , Stellantis CEO and Ford CEO , all of whom made over $20 million last year, about their pay.
"It is time for you to end your greed," Sanders said. "It is time for you to treat your employees with the respect and dignity they deserve. It is time to sit down and negotiate a fair contract."
The independent senator from Vermont has promoted the strikes as a pivotal moment in a broader campaign to raise living standards for working people across the U.S.
"Let us stand together to end corporate greed, let us stand together to rebuild the disappearing middle class, let us create an economy that works for all, not just the one percent," Sanders said.
"Let us all, every American, in every state in this country stand with the UAW," the senator said.
Nearly 13,000 United Auto Workers members went on Friday after the union and the big three automobile manufacturers — , and — failed to reach an agreement Thursday night.
Read more of CNBC's politics coverage:
Workers are targeting three key plants in Michigan, Missouri and Ohio. The strikes are the first time in the labor movement's history that , Ford and Stellantis have been targeted at the same time.
Sanders, a self-proclaimed democratic socialist, made income inequality the central focus of his two unsuccessful campaigns for the Democratic presidential nomination, drawing large crowds at rallies with his uncompromising attacks against corporate America.
Sanders took the helm of the powerful Senate Committee on Health, Education, Labor and Pensions in February. In one of his first acts as chair, he threatened to subpoena CEO Howard Schultz over allegations of union busting.
Sanders said Friday that UAW workers were fighting to bring back the days when unionized automobile jobs were the gold standard for the middle class.
"When you have auto workers who cannot afford to buy the cars they make, that is bad for the economy," the senator said.
UAW President Shawn Fain said earlier Friday that striking workers are "fighting for the justice of the working class." He accused the automakers of "price-gouging" consumers, "ripping off" the taxpayer and "shortchanging" workers.
President Joe Biden, who has sought to closely ally himself with the labor movement, was more measured in remarks delivered Friday but he called on the automakers to ensure "record corporate mean record contracts" for their workers.
The UAW is demanding a 40% hourly wage increase, a 32-hour workweek, the restoration of cost-of-living adjustments, a return to traditional pensions, and the elimination of compensation tiers, among other demands.
Ford said the union's demands would more than double the automaker's labor costs and place the company at a competitive disadvantage compared to non-unionized car companies such as and foreign manufacturers like .
said she was "extremely frustrated and disappointed" with the strikes.