WATCH: President Biden Joins VP Harris On Campaign Trail in Pittsburgh

Joe Biden is the only sitting President in history to have stood on a picket line with striking auto workers. His understanding of the power of unions earned him early endorsements from UAW and its president, Shawn Fain.

When President Biden stepped aside in late July, the same union almost immediately endorsed Vice President Kamala Harris, with Fain appearing in a "Trump Is A Scab" t-shirt during his fiery speech on the opening night of the Democratic National Convention in Chicago last month.

President Biden's career-long support of labor unions will be front and center at his Labor Day parade appearance in Pittsburgh along with the Vice President as he uses his final months in office to support her campaign with Gov. Tim Walz.

It's the first time President Biden and Vice President Harris have both spoken at a campaign event together since she took his place as the Democratic presidential nominee in late July, although both appeared separately at last month's Democratic National Convention.

President Biden and VP Harris are expected to reiterate the White House's stance that Pittsburgh's U.S. Steel should remain domestically owned, despite the company's plans to sell to Japan's Nippon Steel. The President has been firm on this for months, saying in March that localized union workers should be able to keep their jobs.

The President said then, and still believes now, that the company should remain American-owned to "maintain strong American steel companies powered by American steelworkers."

Before they appeared together in Pittsburgh, VP Harris also joined President Biden in the White House’s Situation Room to meet with the U.S. hostage deal negotiating team to discuss their continuing efforts on a deal that would secure the release of the remaining hostages.

The VP also held a Labor Day rally in Detroit before heading to Pittsburgh.