The United Auto Workers union (UAW) is escalating its fight with some of America's biggest carmakers by taking strike action at dozens of parts distribution centres across the US.
UAW boss Shawn Fain said the new walkouts would hit 38 sites owned by General Motors and Stellantis, as the row over pay and benefits continues.
The move excludes Ford, which the UAW said was making more progress in talks.
The UAW declared a strike against the three carmakers last week.
Mr Fain warned that the expansion of the action could lead to delays for customers needing repairs and said he hoped it would raise pressure on the firms to agree new labour contracts.
We're focused on moving the companies at the bargaining table," he said during an online update on the negotiations.
"Right now we think we can get there," he added. "Stellantis and GM in particular are going to need some serious pushing."
This month's strike is the first in the union's history to target all three carmakers - known as the Big Three - at once.
The car companies have said the requests are too onerous. Their most recent proposals include pay rises of roughly 20%.
Last week, President Joe Biden spoke in support of the workers' cause. He said he was sending senior advisers to try to help mediate the dispute, which comes at a time of wider labour tensions.
Mr Fain said on Friday that Ford had agreed to some of the union's demands, such as the reinstatement of automatic pay increases tied to inflation.
The offer of a roughly 20% pay rise was already a "remarkable" gain for the union, Mr Anderson said.
"The UAW has been very successful in identifying what they want, in making the case in front of the public and then systematically exerting the full measure of their capability in a strike," said Mr Anderson.
Car worker JT O'Malley, who has been on strike at a GM assembly plant in Wentzville, Missouri since last week, said he was hopeful that the other two firms would also start to bend.
"I feel like the pressure's getting put on," said the 38-year-old, who has worked at the plant since 2015. "We are energised to make this happen."