LOOMING strike action by the United States’s auto industry workers could test President Joe Biden’s claims that he is the “most pro-union president” in the country’s history.

The United Auto Workers (UAW) has given the nation’s big three auto makers, General Motors, Ford and Stellantis, until midnight tonight for a tentative contract agreement to be reached or as many as 146,000 workers may walk out from their roles.

Last week, Mr Biden repeated his proclamation on CNN that “I’m proud to be the most pro-union president in American history.”

UAW president Shawn Fain, who was elected in March after promising a more confrontational stance in negotiating with car-makers, said Mr Biden has “a lot of work to do in that category.”

He said that the UAW’s demands are about “raising the standard for workers everywhere.

“I truly believe that all of America will stand with us in this fight,” Mr Fain said.

Mr Biden faced some criticism from unions last year when he urged Congress to approve legislation preventing rail workers from going on strike.

But some unions have endorsed him for a second term.

Former Republican president Donald Trump has called on the union membership to back him in the next general election and against Mr Biden’s “all-electric car hoax” which is “built by China.”

His all-caps online post referred to new federal rules requiring two-thirds of new passenger cars sold in the US to be all-electric by 2032.

Mr Trump argued those moves would “murder the US auto industry and kill countless union auto worker jobs forever.”

Mr Fain, who has previously applauded the “transition to a clean auto industry” as long as auto workers “have a place in the new economy,” said Mr Trump was “not someone who stands for a good standard of living.”