WASHINGTON—Prominent labor leaders, frustrated that Democrats in Washington aren't aggressively pursuing the union agenda, are threatening to limit their campaign support for Democrats, an act that would hamper the party's bid to regain control of the House next year and keep a majority in the Senate.

AFL-CIO President Richard Trumka's threat of a pullback Friday was the latest warning to a party that has long relied on labor's cash and grass-roots support. If it makes good on its threat, labor probably would spend more time and money combating union-busting efforts by state officials.

"We will change the way we spend, the way we do things and the way we function that creates power for workers," Trumka said.

In a speech at the National Press Club, Trumka called for "an independent labor movement" and said unions were not responsible for building the power of any political party, but for improving the lives of working families. He promised that unions would spend the summer holding leaders in Congress and the states accountable.

If labor makes itself truly independent of the Democratic Party, it would mark a major shift in a long-standing political relationship.

"It doesn't matter if candidates and parties are controlling the wrecking ball or simply standing aside to let it happen," Trumka said. "The outcome is the same either way. If leaders aren't blocking the wrecking ball and advancing working families' interests, then working people will not support them."

The AFL-CIO's executive council is considering a plan that could spend less on congressional races and more on fighting state battles like those in Wisconsin and Ohio, where lawmakers want to weaken collective bargaining rights and reduce union clout.

But Trumka made clear the federation had no plan to follow the lead of the nation's largest firefighters union, which announced last month that it would halt all political donations to members of Congress because they are not fighting hard enough for union rights. The move has won praise in many corners of the labor movement, where union activists have openly grumbled about House and Senate Democrats being too quiet while unions are getting pummeled in dozens of states.

"We've spent money where we have friends and we will continue to do that," he said.

Leon Fink, a labor historian at the University of Illinois at Chicago, said unions are tired of being taken for granted and discouraged that their influence with moderate and conservative Democrats has been limited.

"Spending a lot of money electing conservative Democrats in marginal districts had no legislative payoff for unions," Fink said. "They don't seem to have the capacity to impose their will on the party."