The firefighter's union, with nearly 300,000 members, is among the most influential and biggest-spending lobbying groups on Capitol Hill. It is also among the most sought-after endorsements for both Democrats and Republicans.

During the 2010 mid-term elections, the union spent nearly $15 million on behalf of federal candidates, including nearly $2.4 million in direct contributions. Its political action committee, known as FIREPAC, was ranked 10th out of more than 7,100 such committees, according to the Center for Responsive Politics.

This year, the firefighters' union is spending millions to stop anti-union legislation in more than half a dozen states. It is working in Ohio to pass a referendum that would overturn the measure eliminating collective bargaining rights for public employees. In Oklahoma, the union is contesting a measure that would ban binding arbitration for firefighters and paramedics. In New Hampshire, firefighters are fighting a bill to make public workers at-will employees. The AFL-CIO has committed to spending about $30 million on fighting such state efforts.

The union is encouraging about 3,500 locals to go along with its freeze on federal political spending. Schaitberger said he would reconsider his decision later this year if Congress becomes more responsive.

There is no indication of other unions following suit so far. Ross Baker, a political science professor at Rutgers University, said he would be surprised if other unions decided to withhold political donations.

"Other than making a very momentary splash, I don't think it's going to embarrass members of Congress into being more supportive of unions," Baker said.

While the move is unusual, it has some precedent. In 2009, the Sheet Metal Workers' union stopped making political donations to members of Congress for about six months to show dissatisfaction with the debate over health reform. The union was irked with lawmakers who considered taxing high-cost health insurance plans enjoyed by some union members. But once the issue was resolved, the union's money to federal candidates began flowing again.

Overall, unions spent more than $200 million in the mid-term elections and about $400 million to help elect President Barack Obama in 2008. Union officials are hoping a backlash against GOP efforts to curb bargaining rights for public workers in Wisconsin, Ohio and other states will help galvanize more support for Democrats at the state and federal level in 2012.

While members of Congress can't control what happens in state legislatures, Schaitberger said he is frustrated that Democrats in particular aren't speaking out.

"The opposition is very focused and our friends, in my view, are not," he said. "Where are the congressional delegations en masse standing up and fighting with us? That's what I see missing."

Schaitberger said he is equally discouraged that pro-union legislation has been bottled up in Congress. Efforts to pass a "card check" bill that would make it easier for workers to form unions went nowhere even when Democrats controlled both houses of Congress. Last year, Senate Republicans blocked a measure that would have granted police officers and firefighters the right to collectively bargain over wages, hours and working conditions.

And other measures have disappointed him, like the lack of money for more emergency response training and equipment for airport fire departments and wilderness firefighting.

"This is a pattern of disappointment," he said. "They have not fulfilled the obligation that friends should have to fight and stand with us and to fight hard on our behalf."