WASHINGTON — President Joe Biden finds himself in a tough spot between his “Union Joe” persona and his aggressive climate goals as the United Auto Workers prepare to strike.

The UAW, which represents 146,000 workers at General Motors, Ford and Stellantis NV‘s North America branch, is ready to strike if their demands are not met by the time their contract expires on Sept. 14. The union is asking for a 46% increase in pay, a 32-hour workweek with 40 hours of pay and the return to a traditional pension system.

Negotiations are not going well. When General Motors on Thursday proposed its largest four-year wage increase in decades, the UAW’s president called the offer “insulting.”

The demands are in part a response to Biden’s electric vehicle policies, which the union says will cost jobs. Proposed Environmental Protection Agency standards for 2027-2032 call for 67% of new vehicles to be electric by the end of the timeframe, in part resulting in a 56% emissions cut.

Biden frequently calls himself “the most pro-union president in American history” and his administration has played a role in resolving several union disputes. Biden on Wednesday had representatives from the International Longshore and Warehouse Union and the Pacific Maritime Association at the White House to celebrate the recent signing of a new contract, which the administration played a role in facilitating.

The UAW is the only major union yet to endorse Biden for re-election. The union has historically supported Democrats and endorsed Biden in 2020.

Speaking on CNBC’s “Last Call” Wednesday, UAW President Shawn Fain said, “Endorsements are earned, not freely given. And actions are going to dictate what we endorse.” Regardless of endorsement, a strike would heavily impact states key to a Biden re-election, like Michigan and Pennsylvania.

Biden irked UAW members on Monday when speaking after a Labor Day event in Philadelphia, Pa. saying he didn’t think a strike was on the horizon. Biden said he was “not worried about a strike until it happens. I don’t think it’s going to happen.”

Fain responded by telling The Detroit News he was “shocked” by Biden’s comments.

“He must know something we don’t know,” Fain said Monday. “As we get down to the wire here, there’s three companies to bargain with and there’s 10 days left to do it. So I know what it looks like to me.”

White House Press Secretary Karine Jean-Pierre on Tuesday said Biden’s comments on the strike were him being “an optimistic person.” She added that Biden believes the UAW is at the “heart of an electric vehicle future that is made in America with union jobs.”

Still, Fain in his interview with “Last Call” went on to tamp down any hopes by former President Donald Trump that an endorsement was on the horizon.

“He was on the air the other day encouraging people to stop paying union dues,” Fain said referring to Trump. “That’s not someone who stands for a good standard of living.”

Fain in the interview also chastised Trump for comments he made during the 2016 election that he said would hurt auto workers.

But Trump is still courting auto workers’ votes. In a statement released Thursday, Trump’s campaign criticized Biden’s electric vehicle policies.

“There is no such thing as a ‘fair transition’ to the destruction of these workers’ livelihoods and the obliteration of this cherished American industry,” the statement said. “Union leadership must decide whether they will stand with Biden and other far-left political cronies in Washington, or whether they will stand with front-line autoworkers and President Trump.”

A strike, Fain told CNBC, would force politicians to “pick a side” in the labor dispute.

“I think a strike can reaffirm to him where the working-class people in this country stand,” Fain said Wednesday. “And it’s time for politicians in this country to pick a side. Either you stand for a billionaire class where everybody else gets left behind, or you stand for the working class. The working-class people vote.”