DETROIT – Leaders of the United Auto Workers are withholding a re-election endorsement for President Joe Biden until the union’s concerns about the auto industry’s transition to all-electric vehicles are addressed, according to a Tuesday letter sent by UAW President Shawn Fain to union staff.

Fain, who was elected union president in March, said the UAW wants a “just transition” for workers. He argues that is currently not the case as automakers invest billions of dollars, with the support of taxpayer money, to move from traditional vehicles to EVs.

“The federal government is pouring billions into the electric vehicle transition, with no strings attached and no commitment to workers,” Fain said in the message obtained by CNBC. “The EV transition is at serious risk of becoming a race to the bottom. We want to see national leadership have our back on this before we make any commitments.”

How to transition traditional auto workers into new jobs for EVs has been a major concern for the UAW for several years. A 2018 study by the union found that mass adoption of EVs could cost the UAW 35,000 jobs, however the union has more recently said that number could be lower.

The UAW has historically supported Democrats, however former President Donald Trump was able to gain notable support from blue-collar auto workers during his presidential campaign.

Fain, in the Tuesday letter, said “another Donald Trump presidency would be a disaster,” citing the need for the union to “get our members organized behind a pro-worker, pro-climate, and pro-democracy political program that can deliver for the working class.”

Biden’s campaign did not immediately respond for comment.

Biden has been a vocal supporter of unions during his presidency, however automakers have increased investments in recent years in states with “right to work” laws.

Fain’s letter, which was first reported by The Detroit News, comes nearly two weeks after he said the union would “back the candidates that support us” in 2024.

Such messaging is a far stronger political stance than the union, which previously endorsed Biden, has taken in recent years, when former leaders and company officials were under a federal corruption investigation.

Fain and other newly elected union leaders ran as reform candidates for the union who would be more vocal and aggressive for its members.

“Right now, we’re focused on making sure the EV transition does right by our members, our families, and our communities,” Fain wrote. “We’ll be ready to talk politics once we secure a future for this industry and the workers who make it run.”

In the letter, Fain singles out the Detroit automakers for recent announcements surrounding plant closures and idling related to EVs turn workers’ lives “upside down.” Most notably Stellantis earlier this year idled a Jeep plant in Illinois citing the need to cut costs to invest in EVs.

Fain also noted the pay rate at a recently opened Ultium Cells LLC battery plant near Lordstown, Ohio – a joint venture battery plant between General Motors and LG Energy Solution – compared to that of traditional automotive assembly plants.

Ultium has said hourly workers currently make between $16 and $22 an hour with full benefits, incentives and tuition assistance. That compares to traditional hourly UAW members that can make upward of $32 an hour at GM plants.

Joint venture battery facilities are viewed as crucial for the UAW to grow and add members, as automakers such as GM transition to electric vehicles, which require less traditional labor and parts than cars with internal combustion engines.

“The situation at Lordstown, and the current state of the EV transition, is unacceptable,” Fain said. “We expect action from the people in power to make it right. I want to make sure our staff are armed and ready with the same tone and message.”