Democratic presidential candidate John Kerry (search) is getting a formidable ally to ward off rival John Edwards' (search) challenges to his position on trade — the labor unions that have been most concerned about U.S. jobs going overseas.

Kerry will get the endorsement of the AFL-CIO (search) at a meeting of union leaders Thursday. The AFL-CIO, comprised of 64 unions representing more than 13 million U.S. workers, is planning an unprecedented effort to mobilize their members to vote for the Massachusetts senator.

The endorsement comes as Edwards begins a tour of key political states that have lost manufacturing jobs. He plans to continue his criticism of Kerry for voting for the 1993 North American Free Trade Agreement (search) that many workers blame for job losses. Edwards said he opposed NAFTA during his 1998 Senate campaign.

"As Senator Kerry himself has pointed out many times during this campaign, records matter," Edwards said. "I think there is a significant difference between us on this issue."

But Kerry said he and Edwards have the same policy on trade. Both voted for normalized trade relations with China and both want to see labor and environmental standards addressed in trade pacts, he said.

Although Edwards said he would have voted against NAFTA, Kerry said: "He wasn't in the Senate back then. I don't know where he registered his vote, but it wasn't in the Senate."

Kerry will pick up the AFL-CIO's endorsement despite his support for free trade, blamed by the unions for eroding their memberships and sending millions of jobs to other countries. But the unions are eager to show a united front headed into November's election after a bruising primary that used millions of labor dollars and exposed deep cracks in the movement.

Teamsters President James P. Hoffa said Kerry has evolved on the issue of trade and has the best chance of beating President Bush.

"He might not be there yet, but I think the more he campaigns, the more he realizes this entire election is going to come down to jobs," Hoffa said in an Associated Press interview Wednesday. "I think he's moving towards that. Everybody evolves."

The Teamsters originally supported Dick Gephardt for president. But the Missouri congressman dropped out after a poor showing in the Iowa caucuses, leaving the Teamsters and 18 other unions that formed the Alliance for Economic Justice with nowhere else to go.

Hoffa said the Teamsters can waver on the trade issue for a candidate with "a total package" who can win in November.

Edwards gave Kerry a scare in Wisconsin's primary Tuesday after highlighting his opposition to NAFTA and Kerry's vote for it. Edwards plans to continue the criticism as the two head toward upcoming nominating contests in Ohio, New York and Georgia.

Kerry, while in Wisconsin, often faced questions about his support of free trade and the movement of jobs overseas. The trend continued Wednesday in Ohio, which Kerry said has lost 160,000 manufacturing jobs since Bush took office.

A woman at a town hall meeting in Dayton said her husband works alongside employees imported from India who will work for a lower wage. Another man talked about his father and grandfather fighting in wars against communism, only to see American companies opening shop in communist countries. Another woman said "fair trade versus free trade" would make the biggest difference in the economy.

In Dayton and in Columbus, Kerry was applauded after promising to review all trade agreements, if elected, to check for worker and environmental protections.

"I pledge to you that we will have not just trade, but smart trade, fair trade, trade where we are giving the American worker a fair playing field to compete on," Kerry said at the Plumbers and Pipefitters Hall in Columbus.