WASHINGTON – Rep. Zack Space, a two-term Democrat running for re-election in Ohio, faces an online campaign urging voters to boycott his candidacy. The pitch isn’t from Republicans or tea party activists.

The website, skipaspace.com, is backed by four unions that say they refuse to work for Space’s return to Congress after he voted against President Obama’s health care legislation.

Leaders of organized labor helped Democrats win the White House and expand their control of Congress two years ago, only to find some candidates they supported didn’t return the favor with votes for the health care measure that passed or a union-organizing bill that stalled. Now, unions say they may spend $88 million on campaigns in the November election, and certain Democrats shouldn’t count on getting a share.

“Each union should have the right to support whoever they want to support based on the issues they care about,” said Karen Ackerman, political director of the 11 million-member AFL-CIO, the largest U.S. labor federation.

Although union leaders say they are determined to keep Congress under Democratic control, they risk undermining that goal by settling scores with incumbents, said Matt Bennett, the White House liaison to governors in the Clinton administration.

“Labor has chosen to take one or two issues and make an example of some Democrats at a moment when control of one of more house of Congress hangs in the balance,” said Bennett, vice president of the Third Way, a group that advocates free trade and deficit controls. “The first off-year election in a Democratic administration is the wrong time to be punishing your friends for insufficient loyalty.”

Space, 49, was one of 34 House Democrats who voted against the health care overhaul this year.

“When accounted for, he took the wrong position,” said Seth Rosen, Cleveland-based regional vice president for the Communications Workers of America. “Our activists’ energy is not a blank check that people can take for granted. We’re not part of the Democratic Party.”

Andrew Ricci, communications director for Space’s campaign, said: “We’re not going to pick a fight with anyone because they don’t agree with us one time, when 99 percent of the time we share their priorities.”

Unions are also sitting out two House races in New York and a Senate race in Arkansas.

Rep. Chris Van Hollen, D-Md., chairman of the Democratic Congressional Campaign Committee, said unions and Democratic leaders “have had our differences.”

“The stakes are high for working Americans, and we simply cannot afford letting Republicans bring back the exact same disastrous economic agenda that drove the economy into a ditch,” Van Hollen said.

The AFL-CIO’s Ackerman said: “We want to hold individual Democrats accountable to our members. But when you look at the big picture, the possibility of a Speaker Boehner – who trashes workers as special interests – it’s horrifying.”