The United Auto Workers (UAW) will expand its strike Friday afternoon, with employees walking off the job at General Motors and Stellantis parts distribution facilities, union President Shawn Fain announced.

Fain, in livestreamed remarks, said workers have made progress in negotiations with Ford since a targeted strike began at the Big Three auto companies last week. 

“At GM and Stellantis, it’s a different story,” Fain said.

The union is expanding the strike Friday to include Stellantis and GM facilities at 38 locations across 28 states, he said.

“We will shut down parts distribution until those two companies come to their senses and come to the table with a serious offer,” Fain said.

The expanded strike could threaten economic gains and poses a growing problem for President Biden, who is staunchly pro-union but has backed policies to incentivize the use of electric vehicles, which is a factor in the strike.

Fain on Friday extended an invitation to Biden to join workers on the picket line.

“We invite and encourage everyone who supports our case to join us on the picket line, from our friends and families all the way up to the president of the United States. We invite you to join us in our fight,” he said.

Autoworkers represented by the UAW went on strike at a small number of factories last week after the union failed to reach a deal with General Motors, Ford and Stellantis.

The union is asking for increased pay and benefits, as well as more security for part-time staffers. Also at issue is the fate of union members as auto companies increasingly transition toward manufacturing electric vehicles.

Biden in remarks last week called on auto companies to share “record profits” with their workers.

“Over generations, autoworkers sacrificed so much to keep the industry alive and strong, especially through economic crises and the pandemics. Workers deserve a fair share of the benefits they helped create for an enterprise,” he said.

Biden also designated acting Labor Secretary Julie Su and senior adviser Gene Sperling as liaisons amid the strike. Su and Sperling were initially expected to travel to Detroit, but the White House this week announced they would remain in Washington, D.C., and engage with the two sides remotely amid ongoing negotiations.

Meanwhile, former President Trump is planning to travel to Detroit next week to give a speech instead of attending the second GOP primary debate, aiming to show support for union workers in a key swing state. Fain, however, has been sharply critical of Trump, and the former president is unlikely to appear on the picket line.

Polling immediately after the UAW first went on strike showed public support for the workers has ticked up slightly. A Morning Consult poll showed 54 percent of adults support the striking workers, up from 51 percent pre-strike.

“Our message to the consumer is simple: The way to fix the frustrating customer experience is for the companies to end price gouging,” Fain said Friday. “Invest these profits into stable jobs and sustainable wages and benefits.”

Updated at 10:48 a.m. ET