The vice president donned a black-and-gold United Steelworkers union hat and told hundreds of union members that the gap between the wealthy and poor was hurting the nation.
"The tax code's not fair. It's simply not fair," Biden said in a city long associated with organized labor. "The wealthy aren't paying their fair share. There used to be one America."
Biden later marched throughout the city's downtown, hearing encouraging words along the parade route.
"Give it a go, Joe!" shouted one woman.
Biden is seriously considering a late entry into the 2016 Democratic presidential campaign. His entry could jumble a Democratic contest that has seen front-runner Hillary Rodham Clinton's lead diminish in early states against Vermont Sen. Bernie Sanders, an independent who describes himself as a democratic socialist.
Underscoring the volatile nature of the race, an NBC News poll released Sunday showed Sanders gaining an advantage over Clinton in New Hampshire, a state where Bill and Hillary Clinton have maintained deep ties during their political careers.
Biden, however, said last week he wasn't certain if he and his family had the "emotional energy" for another campaign.
But AFL-CIO President Richard Trumka, who walked the parade route with Biden, said the vice president got a strong response from the city's workers.
"If you're looking for energy, this is a great place to get energy today," the labor leader said.