The largest collection of US labor unions endorsed Joe Biden for the White House Tuesday, saying President Donald Trump let workers down and has been "delinquent" in his coronavirus response.

"We know Joe, and Joe knows us," AFL-CIO president Richard Trumka said of the 12.5 million members and 55 unions that comprise the grouping.

The former vice president has "marched on our picket lines" to help improve conditions for the American worker, Trumka added.

The endorsement is not just an expression of support for Biden, whom Trumka described as a man of his word and a champion for health care, living wages, civil rights and the ability to form and join a union.

"It's also a clear rejection of our current trajectory," Trumka said.

"Donald Trump campaigned as a friend of workers" and managed to draw votes from working-class Americans "desperate for a departure from business as usual," Trumka added.

But over the past three-plus years, "the president showed his true colors," slashing rules to protect workers, cutting safety inspectors and undermining collective bargaining.

"His response to COVID-19 has been delinquent, delayed, disorganized and deadly," Trumka said, adding that Trump has played on the worst fears of Americans.

"That's our choice this year, between Donald Trump's pettiness and negativity and Joe Biden who is the embodiment of goodness and decency."

The AFL-CIO has endorsed the Democratic candidate in every presidential election since 1976.