Harris and Biden Will Make a Labor Day Pitch to Union Voters

President Biden and Vice President Kamala Harris will appear together on Monday in Pittsburgh to celebrate labor unions, a crucial mobilizing force for Democrats, at their first joint campaign event since Ms. Harris replaced Mr. Biden at the top of the ticket in July.

Mr. Biden has called himself the most pro-union president in history, and last year he became the first sitting president to visit a picket line.

Now Ms. Harris is hoping to adopt that pro-worker mantle for herself. As vice president, she led a task force examining the ways that the government could help expand union membership. But business leaders generally see her as friendlier to their interests and more flexible on policy than Mr. Biden.

In Pittsburgh, Ms. Harris and Mr. Biden will attend an event at a local union hall alongside Gov. Josh Shapiro of Pennsylvania and Senator Bob Casey, who is up for re-election. The Harris campaign said local and national leaders of major unions including the International Brotherhood of Electrical Workers, the A.F.L.-C.I.O. and the United Steelworkers will attend.

Earlier in the day, Ms. Harris is set to hold an event in Detroit, another union stronghold in a battleground state. She will be joined by Gov. Gretchen Whitmer of Michigan, as well as two of the nation’s most prominent labor leaders, Randi Weingarten of the American Federation of Teachers and Shawn Fain of the United Automobile Workers. Her running mate, Gov. Tim Walz of Minnesota, will appear in Milwaukee.

Although Ms. Harris and Mr. Walz will reach voters in three of the top swing states, the events themselves will be smaller than the rallies Ms. Harris has held in recent weeks that have drawn thousands of attendees. She and Mr. Biden are expected to deliver “informal remarks” rather than full speeches, according to the Harris campaign.