Biden responded in a tweet of his own: "I'm sick of this President badmouthing unions. We are in a battle for America's soul, I really believe that, and I want to restore it", he said.
Biden picked up the endorsement of the Pittsburgh-based International Association of Fire Fighters Local No. 1 earlier Monday morning.
The American banker, who now serves on the board of the Obama Foundation, appeared Monday morning for an interview on the Fox News show America's Newsroom to discuss the former vice president's campaign for his party's nomination for president.
"He represents the labor force and the middle class", said Bill Vrana, 55, a member of Teamsters 249 that hosted the Biden rally.
He explained that Biden is the best candidate to defeat Trump in Wisconsin, Michigan and Pennsylvania, all narrowly won by Trump in 2016 over Hillary Clinton.
"There was a $2 trillion tax cut, did you feel it?"
The fervor inside the Teamsters union hall combined a nostalgia for President Obama with the conviction that Mr. Biden was electable and a belief that the former vice president would be a transitional figure on the way to the far-left government envisioned by party activists.
He also complained about Biden receiving the firefighters' union's endorsement. He then called out President Trump, who has trashed Biden as "very weak".
Pennsylvania will be a key battleground in the 2020 general election, and Biden is making an early play in the state.
In a series of tweets Monday morning, the president railed against the Biden and the union describing the organization's leaders as "Dues Crazy".
In a race dominated by discourse around major progressive policies like the Green New Deal and universal healthcare, Biden - who is often lauded for his working class charm - is betting his moderate appeal will gain him widespread support. Minimum wage, overtime pay, the 40-hour week: they exist for all of us because unions fought for those rights.
Voters in Pittsburgh, though, said they would love to go back to the future. "We need to start seeing action". Trump was the first Republican presidential nominee to win the state since President George H.W. Bush in 1988.
Biden's first week on the campaign trail will also include a two-day swing through Iowa, with events planned for Tuesday in the eastern part of the state and Wednesday in central Iowa.