Sen. Obama, of Illinois, and Republican rival Sen. John McCain, of Arizona, are vying for the support of unions in key battleground states such as Michigan, Ohio and Pennsylvania, The Detroit News reported Monday.

"Senator Obama is using the Detroit Labor Day kickoff to emphasize three messages: addressing the needs of working people, the key role unions play in the election, and the role of manufacturing and the auto

industry," said Harley Shaiken, a professor of labor studies at the University of California-Berkeley, noting most unions are backing Obama.

Robert Reich, the labor secretary under President Bill Clinton, said he believes union turnout will be "very high" this year because union households have been hit hard by the poor economy.