The United Automobile Workers union is expanding its targeted strike against two Detroit automakers as the walkout enters its second week.
Shawn Fain, the union’s president, said Friday that workers at 38 spare parts distribution centers at General Motors and Stellantis would walk off the job at noon.
“We will shut down parts distribution centers until those two companies come to their senses and come to the bargaining table,” Mr. Fain said.
The locations affected include all the parts distribution centers at G.M. and Stellantis, but does not include any new facilities at Ford Motor, which Mr. Fain said had gone further in meeting the union’s demands.
“To be clear we are not done at Ford,” he said. “We have serious issues to work through but we do want to recognize that Ford is serious about reaching a deal.”
Tensions between the union and the automakers had flared up even before Mr. Fain announced the expansion of the strike. On Thursday, private messages sent by a union communications manager via X, formerly known as Twitter, seemed to suggest that the union leaders were pleased that the strike appeared to be hurting the three manufacturers.
Jonah Furman, who was hired to direct the U.A.W.’s media relations after Mr. Fain took office this year, wrote in the messages that the strike was causing the automakers to suffer “reputations damage and operational chaos.”
The contents of the messages were revealed in The Detroit News.
G.M. said in a statement that the leaked messages showed a “callous disregard for the seriousness of what is at stake” in the strike.
“It’s now clear that the U.A.W. leadership has always intended to cause monthslong disruption, regardless of the harm it causes to its members and their communities,” the company added.
The expansion of the stoppage heightens the stakes for both sides, and could force other plants owned by the automakers and their suppliers to halt production.
The union is paying striking workers $500 per week each from its $825 million strike fund, while the manufacturers are faced with losing tens of millions of dollars in revenue every day that the affected plants remain idled.
A week ago, the union called on workers to strike at a G.M. pickup truck plant in Wentzville, Mo.; a Ford factory in Michigan that makes the Bronco sport-utility vehicle; and a Jeep plant in Toledo, Ohio, owned by Stellantis.
The union is seeking a substantial increase in wages, noting that the automakers have reported strong profits in the last 10 years and have raised the pay of their chief executives. The union initially demanded a 40 percent increase; the companies have offered about 20 percent over four years.
The U.A.W. also wants more workers to qualify for pensions, company-paid retiree health care, shorter working hours and job security for workers if the manufacturers close plants in the future. It also wanted to end a wage system in which new hires start at about $17 an hour, and must stay on the job eight years to climb up to the top wage of $32 an hour.
Peter Berg, a professor of employment relations at Michigan State University, said the U.A.W.’s strategy of limiting strikes to certain locations eases the cost of supporting workers from its strike fund, but hurts the manufacturers because those plants make some of their most profitable vehicles.
“The question is, can the union maintain solidarity and keep everyone together if this continues for several more weeks,” he said.
Earlier in the week, workers demonstrating at Stellantis’s North American headquarters in Auburn Hills, Mich., said they were energized and ready to join the walkout, if called to do so.
“President Fain has got fight,” said Marnice Alford, who works in the paint shop at a Stellantis plant in Sterling Heights, near Detroit. “I like that.”
This is a developing story. Check back for updates.