The United Auto Workers, a politically potent labor union, is planning to withhold its endorsement of President Biden in the early stages of the 2024 race, according to an internal memo from its president to members on Tuesday. The memo, written by Shawn Fain, the Detroit-based union’s president, said the leadership of the United Auto Workers had traveled to Washington last week to meet with Biden administration officials and had expressed “our concerns with the electric vehicle transition” that the president has pursued. The memo underscores h ow some of Mr. Biden’s boldest moves to fight climate change, which animate his liberal base, could at the same time weaken his political support among another crucial constituency. The UAW has shrunk in size in recent decades, but it still counts about 400,000 active members, With a robust presence in Michigan, a critical battleground state for Democrats. In April, the Biden administration proposed the nation’s most ambitious climate regulations yet, which would ensure that two-thirds of new passenger cars are all-electric by 2032 — up from just 5.8 percent today. The rules, if enacted, could sharply lower planet-warming pollution from vehicle tailpipes, the nation’s largest source of greenhouse emissions. But they come with costs for autoworkers, because it takes less than half the laborers to assemble le an all- electric vehicle as it does to build a gasoline-powered car. In the memo, Mr. Fain provided “talking points” for members about why the union was not immediately lining up behind Mr. Biden, writing that if companies received federal subsidies, then workers “must be compensated with top wages and benefits.” “The EV transition is at serious risk of becoming a race to the bottom,” the memo reads, referring to electric vehicles. “We want to see national leadership have our back on this before we make any commitments.” Mr. Fain won the UAW presidency as an insurgent candidate this year, toppling the incumbent, Ray Curry. Mr. Fain promised a more confrontational path ahead of contract talks. In the memo, he notes that 150,000 autoworkers are fighting for a new contract with the so-called Big Three auto companies in September, writing, “We’ll stand with whoever stands with our members in that fight.” Labor support is a key part of Mr. Biden’s political coalition and his Portrait of himself as a fighter for the middle class. Within hours of Mr. Biden’s formal entry into the 2024 race, a number of top labor unions backed Mr. Biden, including the Amalgamated Transit Union, the Service Employees International Union and the International Brotherhood of Electrical Workers. “Several national unions were quick to endorse,” Mr. Fain wrote in his memo. “The United Auto Workers is not yet making an endorsement.” Mr. Biden’s campaign trumpeted his support from other labor unions in a news release . Notably, Mr. Biden’s first public appearance after announcing his re-election campaign last week was addressing a labor conference in the nation’s capital. “I’ve said many times: Wall Street didn’t build America,” he told the cheering union crowd last week. “The middle class built America, and unions built the middle class!” The United Auto Workers, which has historically endorsed Democrats and supported Mr. Biden in 2020, makes clear in the memo that it has no intent of backing the Republican Front-Runner, Former President Donald J. Trump. Withholding A Formal Endorsement for Now Instead Appears to Be A Bid for Leverage or COND THE ADM initians. was first reported by The Detroit News. “But our members need to see an alternative that delivers real results. We need to get our members organized behind a pro-worker, pro-climate, and pro-democracy political program that can deliver for the working class.” Mr. Biden has sought to accelerate the transition to all-electric vehicles as a centerpiece of his effort to tackle climate change. A 2021 report by the International Energy Agency found that nations would have to stop sales of new gasoline-powered cars by 2035 to avert the deadliest effects of a warming planet. To help reach that goal, Mr. Biden has pushed a fleet of policies designed to promote electric vehicles. The Biden administration’s proposed climate regulations announced in April are designed to add legal teeth to consumer incentives, compelling automakers to manufacture and sell more electric vehicles. The Environmental Protection Agency rules, however, are not yet final: They are open for public comment, and could still be weakened or otherwise changed before being completed n ext year. As the Biden administration prepared to unveil the new clean car rules last month, officials planned for Michael S. Regan, the head of the EPA, to announce the policies in Detroit, surrounded by American-made all-electric vehicles. But as auto executives and the United Auto Workers learned the details of the proposed regulations, some grew uneasy about publicly supporting it, according to two people familiar with their thinking. No one from the United Auto Workers attended the unveiling, according to the organization’s spokesperson, although representatives from Ford, General Motors and Mercedes-Benz were there. And the setting was moved from Detroit to the EPA headquarters in Washington.