The powerful United Auto Workers (UAW) formally endorsed Joe Biden’s re-election campaign on Wednesday at the union’s national community action program conference in Washington DC.

Both the US president and rival Donald Trump have courted the union and supported its successful strike action against the US’s big three automakers last year. Biden became the first president to walk a picket line in support of the union.

“Joe Biden bet on the American worker while Donald Trump blamed the American worker,” UAW president, Shawn Fain told the conference. “If our endorsement must be earned, Joe Biden has earned it.

“Donald Trump is a scab. Donald Trump is a billionaire and that’s who he represents,” Fain said. “This election is about who will stand up with us and who will stand in our way.”

The conference is where the UAW’s delegates and leaders develop and shape the 40,000-strong union’s political and legislative priorities. It is the union’s first conference with Fain at the helm since he was elected president of the union on a reform slate in March 2023.

Addressing the conference, Biden said: “I honest to God have always believed the union movement in America is important because it produces the best skilled workers in the world. It’s good for everybody.”

“Our plan is delivering for the American people, building an economy from the middle out and the bottom up, not the top down,” he continued. “When Donald Trump was in office, six auto factories closed around the country. Tens of thousands of auto jobs were lost nationwide during Trump’s presidency. During my presidency, we opened 20 auto factories and more than 250,000 auto jobs all across the country.”

Fain has been strongly critical of Trump. This week he said Trump was “pretty much contrary to everything we stand for”. But the UAW has many Trump-supporting members and the union had held off on endorsing Biden.

Biden has repeatedly touted himself as the most pro-labor president in history and joined the picket line of striking UAW members during the “standup” strikes at the big three automakers in September, becoming the first sitting president to join a picket line.

Last week Sean O’Brien, the president of the Teamsters union, announced he had met privately with Trump in a move that progressive members called “a slap in the face”.

Biden has also received the endorsements from the AFL-CIO, the largest federation of unions in the US, and the National Education Association, which represents about 3 million educators, the largest union in the US.