Former Vice President Joe Biden speaks at a rally in Collier, Pennsylvania, March 6, 2018. Credit: Gene J. Puskar | AP

Former vice president Joe Biden won the backing Monday of the International Association of Fire Fighters, nailing down the support of the first major labor union to offer an endorsement in the crowded Democratic race for the White House.

The endorsement was widely expected, as members held “Run Joe Run” signs when Biden addressed the group at a conference in Washington last month. But the announcement — by way of a video — offers Biden a boost as he prepares to hit the campaign trail Monday with a rally in Pittsburgh, where he is seeking to court the working class in a state carried by President Donald Trump in 2016.

“Joe’s a lot like our firefighters,” Harold Schaitberger, the IAFF’s general president, said in the video. “He’s a problem solver who cares deeply about America and committed to making our country better. He’s one of the staunchest advocates for working families. He knows that a strong middle class means a strong America, and we know, as president, he will stand up for all the patriotic Americans who want nothing more than to earn a decent wage, send their kids to college, have affordable health care and a decent and secure retirement.”

The IAFF stayed out of the 2016 election, declining to endorse Democrat Hillary Clinton in her bid against Trump.

Biden had yet to announce when he appeared before the IAFF in mid-March, but he seemed to tip his hand to the enthusiastic crowd.

“I appreciate the energy you showed when I got up here,” he said upon taking the stage. “Save it a little longer. I may need it in a few weeks.”

Biden is expected to be joined in Pittsburgh on Monday by members of the United Steelworkers. The union’s president, Leo Gerard, told reporters recently that it will be “out in force.”

But other unions are holding back their endorsements for now, taking time to evaluate a field in which many candidates are seeking their support.

Washington Post writer David Weigel contributed to this report.