Former Sen. John Edwards is expected to start his Labor Day in Pittsburgh and leave with the endorsement of the United Steelworkers.

Mr. Edwards has courted the USW and other unions since the end of his 2004 vice presidential candidacy, which was publicly launched in Mellon Square, just blocks from the Mellon Arena site of the Monday rally where the former North Carolina senator will speak before the start of the Labor Day parade.

Neither the Edwards campaign nor the USW responded to inquiries about the planned announcement, which still must be formally confirmed in a conference of the USW's executive committee.

The former senator is to speak at 9 a.m. before heading to Iowa, site of the opening caucuses of the 2008 presidential battle.

The USW support will be announced at a time when major labor organizations are heading off in a variety of directions in the nomination battle. On Wednesday, the International Association of Firefighters made the surprise move of lining up behind Sen. Chris Dodd, D-Conn., who has been regarded as a long shot in the Democratic competition. Yesterday the International Association of Machinists announced its support for Sen. Hillary Clinton, D-N.Y., while Mr. Edwards received the endorsement of the United Brotherhood of Carpenters and Joiners of America.

Ms. Clinton has enjoyed consistently large leads in early national polling in the presidential race. Mr. Edwards, however, has shown polling strength in Iowa, support that he hopes will vault him to the front of the race in the intense stretch of early balloting leading into the Feb. 5 mega-primary, when delegates will be chosen in 20 states across the country.

Mr. Edwards' last public appearance in Pittsburgh was this summer, at the Hill House, where he stopped on a tour designed to highlight the issues of poverty that have been a core theme in his presidential bid.