President Obama's visit comes amid tight governor's race
Union membership has plummeted in Wisconsin over the four years since Obama last attended the labor rally in Milwaukee, thanks to the 2011 law that effectively ended collective bargaining for most public workers.
The president's appearance Monday comes as the architect of that law, Governor Scott Walker, is locked in a tight re-election battle against Democrat Mary Burke.
She will also attend the event, but is not speaking. Instead, Burke will meet privately with Obama.
Republicans say Burke is running from Obama, whose approval rating in Wisconsin has dropped below 50 percent.