BOSTON (AP)- Republican incumbent Scott Brown and Democratic challenger Elizabeth Warren are honing their campaign pitches to union workers as they scrap for every vote in Massachusetts' U.S. Senate race.
While Warren has the backing of the AFL-CIO and has appeared with union activists on the campaign trail, Brown is courting rank-and-file workers and scooping up his own endorsements, many from police organizations.
Brown is facing more than just a battle of endorsements, however.
The AFL-CIO's support of Warren brings with it a small army of campaign workers and financial support. The group has already helped flood voter mailboxes with fliers promoting Warren's candidacy.
Warren has been aggressive about courting union votes.
Last month, she accepted the backing of the Professional Fire Fighters of Massachusetts outside a fire station in the city's South Boston neighborhood.
"I know that if anything goes wrong, the firefighters of the commonwealth of Massachusetts have my back," she said. "I guarantee you if I go to Washington, I'll have their back."
Brown also has reason to hope his message to union workers is resonating.
AFL-CIO officials have acknowledged nearly half their members voted for Brown in the 2010 special election when he won the seat left vacant by the death of longtime Democratic U.S. Sen. Edward Kennedy.
Those union votes went to Brown despite the AFL-CIO's endorsement of Brown's Democratic rival, state Attorney General Martha Coakley.
Brown is hoping to repeat that support. Last week he held a campaign event in Worcester to accept the endorsement of Carl Gentile, former president of the Worcester's Teamsters Union.
Gentile praised what he called Brown's ability to work with Republicans and Democrats.
"I know that my union is not happy with the decision I made," he said. "But you have to cross over that center lane. You have to be a bipartisan, and nobody does it any better than Scott Brown."
Brown has also touted the backing of police groups like the Massachusetts Municipal Police Coalition, a voluntary coalition of municipal police unions in communities around greater Boston.
Brown welcomed the support, saying, "The interests of law enforcement have always been near and dear to my heart."
In fundraising letters, Brown has also tried to appeal to union members over the heads of union officials.
"Big Labor Bosses are forcing union members to get-out-the-vote for Elizabeth Warren or get fined," he wrote. "Outside groups like the AFL-CIO and EMILY's List have sent hateful mail to households across the state wildly distorting my record."
Union officials, who have disputed fining members, have almost as much riding on the outcome of the election as the candidates.
Massachusetts AFL-CIO President Steven Tolman said the group has been working hard to educate members about Brown's record.
"When we did need his vote, he was not with us," Tolman said, pointing one of Brown's first votes - his opposition to President Barack Obama's choice of a union attorney Craig Becker for the National Labor Relations Board.
Tolman, who served in the Massachusetts Senate with Brown, said Brown was a more reliable vote at the Statehouse and even won the AFL-CIO endorsement when he ran for re-election in 2008.
Tolman also said trying to get union workers to back Warren, a Harvard Law professor, isn't as hard as it might seem.
"She's out there saying she's proud to have labor support," he said. "She's got a backbone."
In recent days, Brown has opened a new line of criticism, pointing to a tax on high-cost health insurance plans - a so-called Cadillac tax - that's part of the 2010 federal health care law that Obama signed and Warren supports.
Brown, who has called for the law's repeal, argues that the tax could also affect insurance policies for unions including those covering firefighters, police and teachers.
A Warren spokeswoman said she wouldn't have advocated for the tax but supports the law because it lowers health care costs and eases the burden on middle-class families.
Warren has won strong union support in her fundraising drives.
Among the political action committees that have given Warren $10,000 this election cycle was a PAC associated with the United Auto Workers.
Other PACs that have given Warren $5,000 or more include those associated with the American Federation of Teachers, the International Brotherhood of Electrical Workers, the International Brotherhood of Boilermakers, the Transport Workers Unions of America and the International Association of Heat and Frost Insulators and Asbestos Workers.
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