A United Auto Worker cheers at cars as they pass outside an entrance to the Stellantis's factory where the Jeep Wrangler and Gladiator are built in Toledo, Ohio on Monday, September 18. (Aaron Josefczyk/UPI/Shutterstock)

New York (CNN) — The United Auto Workers union is expanding its strike against GM and Stellantis but said that progress in negotiations with Ford means it won’t expand the number of Ford workers on the picket lines.

UAW President Shawn Fain made the announcement on Friday morning. “At noon Eastern today, all parts distributions centers at General Motors and Stellantis will be on strike,” 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.”

But Fain said that there has been significant improvement in offers from Ford and that is the reason the strike will not be expanded there.

“We do want to recognize that Ford is serious about reaching a deal,” he said.

The strike will now expand to GM’s and Stellantis’s 38 parts and distribution centers spread across 20 states. The distribution centers generally send parts to dealerships to be used for repairs, so the move could quickly cripple dealerships ability to do repairs, which is the most profitable part of their business.

GM criticized the union’s latest walkout announcement in a statement.

“UAW leadership needs to put the interests of its members and the country over their own ideological and personal agendas,” the company said. “We’ve put a 5th record offer on the table and are ready, as we always have been, to bargain in good faith to reach a deal that rewards our team members and allows GM to succeed and thrive into the future.”

Still the announcement of progress at Ford raised hopes that the strike, at least at there, could be brought to a relatively quick end. Before Friday, there had been few public signs that the union and management of the three companies were anywhere close to an agreement.

“We continue to negotiate with the UAW. Our focus has not wavered on reaching a deal that rewards our employees, allows us to create great value for customers from Ford’s unique position as the most American automaker and enables Ford to invest and grow,” Ford said in a statement.

The announcement comes just days after Ford reached a tentative deal with the Canadian union Unifor, which averted a strike by more than 5,000 autoworkers in that country that would have should down its three factories there.

While the strike will continue at the three assembly lines already on strike – a Ford truck plant in Wayne, Michigan, a GM plant in Wentzville, Missouri and the Stellantis in Toledo – there will be no additional factories added, only the parts distribution centers. But that will create great pressure on GM and Stellantis from their network of dealerships.

The union had started the strike on September 15 with strikes at only three of the companies’ 25 US assembly plants, having about 12,700 of its 145,000 members at the traditional “Big Three” walk off early that morning.

This is the first time the union has struck all of the Big Three automakers at the same time. Traditionally it has picked one company at a time as a target for its job actions. And most often, it has had all the workers at that company going on strike at the same time.

As of 10:30 am ET, Stellantis (STLA) is up 0.98%; Ford (F) is up 3.57%; and GM (GM) is up 0.7%.