The United Auto Workers on Friday widened its strike against General Motors and Jeep-maker Stellantis out of frustration over contract talks, while sparing more Ford locations, citing progressing negotiations with the company. President Joe Biden also announced he will join a picket line in Michigan next week to support the UAW.

Union workers walked out of 38 GM and Stellantis parts distribution centers in 20 states just after noon on Friday to "shut down parts distribution until those two companies come to their senses and come to the table with a serious offer," UAW President Shawn Fain said. The strike escalation adds about 5,600 workers to the work stoppage, for a total of 18,300 - about 12 percent of the UAW's autoworker members.

Biden said he will "stand in solidarity with the UAW" on Tuesday on social media. He would probably be the first president to join a picket line in at least 100 years.

The Post first reported news of Biden going to Michigan earlier on Friday. Union leaders invited Biden to join the picket line earlier on Friday.

The strike began a week earlier at three auto manufacturing plants, one for each company, but the expansion is focused on the warehouses that send parts to dealerships and others for vehicle repairs, meaning Americans who drive Jeeps and Chevy Silverados could begin to feel the strike's impact.

Speaking alongside striking workers at a Stellantis warehouse in Center Line, Mich., Fain said the distribution centers "generate a lot of profits, especially for Stellantis."

Fain said the union will not widen the strike against Ford for now, because Ford has made further concessions, and negotiations are progressing. He said Ford had agreed to reinstate cost-of-living adjustments to wages and offer new job-security provisions. The union is continuing its current strike against one Ford factory in Michigan, however.

The strike had originally targeted three vehicle-assembly factories in Michigan, Missouri and Ohio that assemble the Ford Bronco, the Chevrolet Colorado and the Jeep Wrangler. The broadened strike dramatically increases the footprint of the work stoppage with GM and Stellantis warehouses in or near cities across the nation: Denver, Chicago, Los Angeles, Cincinnati, Orlando, Boston, Reno and beyond.

Fain said many warehouse workers are stuck on a lower pay scale than assembly-plant workers. Those hired after 2015 max out at $25 an hour after eight years of work, he said. GM has offered to convert those workers to the top wage tier, Fain said, but he added that "without cost-of-living and job security like we won at Ford, those members are still at serious risk."

Outside a Stellantis parts warehouse in Ontario, Calif., which employs 138 people, local union president Jesse Ramirez on Friday joined a couple dozen people waving signs.

With housing prices spiking in California, Ramirez said he and many other workers at the facility have commutes of at least an hour from communities they can afford to live in. Ramirez is married with four kids and his wife works as a dental manager, but even with two salaries "it's a lot harder now," he said.

Ramirez also complained about the company outsourcing jobs to nonunion workers. "Little by little they're outsourcing our jobs to the point where there will be no one left in the building," he said.

An expanded work stoppage over wages and benefits is expected to exacerbate disruptions to an industry that makes up about 3 percent of the nation's gross domestic product.

The union is seeking a 36 percent wage increase over four years, improved retirement benefits, more paid time off and other perks. Full-time UAW workers today earn $18 to $32 an hour, plus annual profit-sharing bonuses that have totaled tens of thousands of dollars per worker over the last four years. Temporary workers earn $16 to $19 an hour and don't get bonuses.

All of the automakers are offering raises of around 20 percent over four years and other perks that they say constitute their best offers to the union in decades. They argue they can't meet all of the UAW demands and remain viable companies capable of investing in the new factories needed for the costly transition to electric vehicles.

Ford said in a statement Friday it is working "diligently with the UAW to reach a deal that rewards our workforce and enables Ford to invest in a vibrant and growing future." It added: "Although we are making progress in some areas, we still have significant gaps to close on the key economic issues. In the end, the issues are interconnected and must work within an overall agreement that supports our mutual success."

GM called the strike escalation "unnecessary" and accused union leaders of "manipulating the bargaining process for their own personal agendas."

"We have now presented five separate economic proposals that are historic," the company said. The 20 percent raise in its latest offer would boost 85 percent of GM's UAW workforce to base-wage earnings of $82,000 a year by the end of the contract, the company said this week. It is also offering two weeks of paid parental leave and other perks.

Stellantis said it submitted a new offer to the UAW on Thursday but has not received a reply. In addition to a 21 percent "compounded increase" to wages over the course of a new contract, the offer promises "a long-term solution" for a factory the company shuttered earlier this year in Belvidere, Ill., and other perks, Stellantis said. It questioned "whether the union's leadership has ever had an interest in reaching an agreement in a timely manner."

"They seem more concerned about pursuing their own political agendas than negotiating in the best interests of our employees and the sustainability of our U.S. operations given the market's fierce competition," the company said.

Fain said Ford has made important new concessions in recent days, including agreeing to reinstate the cost-of-living adjustments to wages that the union lost around the time of the Great Recession.

"Many people said this couldn't be done, and we just did it," Fain said.

Ford has also agreed to let workers strike over any plant closures during the life of the next contract - a concession that no automaker has allowed before, Fain said.

"I don't have to tell you that this is an important victory in our fight to save our jobs, keep families together, to keep our communities from being gutted," he said.

UAW officials previously communicated to the Biden administration that a Biden visit to the picket line would be welcome, but they had not formally invited the president to attend. Union leadership had been frustrated by Biden's announcement last week that the White House was dispatching two aides to the talks - a trip that was later canceled after the UAW leadership told the administration to either join the picket line or not come at all.

Fain also publicly invited everyone, "all the way up to the president of the United States," to come to the picket line during the Facebook Live event. Michigan Democrats and other Biden allies had been pressuring him to join the strikers.

Donald Trump, Biden's likely 2024 presidential rival, has announced he will hold a rally in Detroit next week during the second GOP primary debate. Trump has not said whether he will attempt to join the picket line, but Fain has been clear that the former GOP president would not be welcome there.

Several workers demonstrating outside the Ontario, Calif., warehouse expressed anger at how corporate profits have ballooned while their salaries have not even kept up with the cost of living.

"They're making record profits and we're not seeing that here," said Fred Miranda, 62, a 20-year employee at the plant. "We can't afford to buy our own cars we supply the parts for."

Miranda and other longtime workers are known as "legacy employees." They can make over $30 an hour. But several are convinced the company would like to replace them through buyouts or other means to hire cheaper replacements.

"They're trying to get rid of the legacy employees," said Perry Rhodes, 59, who has worked at the plant for 27 years and makes $31 an hour.

Under the tiered system, several employees explained, it takes eight years to get up to $25 an hour. But they said the company manages to avoid even that by labeling people "temporary workers" or "summer employees" so even after eight years they still are making less than $25 an hour.

"The little guys are tired of being bullied by big corporations," said Jasmine Shoulders, 31, another worker at the facility.

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Lauren Kaori Gurley contributed to this report.