By Rachelle Younglai

WASHINGTON (Reuters) - The country's largest labor federation warned the Obama administration and congressional Democrats not to take their support for granted and said they would work against any elected leader who supports pending free trade agreements.

"Every elected leader will be held accountable," AFL-CIO President Richard Trumka told reporters, as anti-Wall Street protests spread across the United States.

"Working families will be demanding action to promote a real job creation agenda. They are not going to go away," he said.

Unions have started joining protesters angry about home foreclosures, high unemployment, executive compensation and the 2008 financial services bailout. The demonstrations, which started in New York a few weeks ago, have since spread to Los Angeles, Philadelphia, Florida, Chicago and other cities.

The AFL-CIO is pushing for a tax on financial speculation, that it said will provide revenue to invest in jobs, schools and roads. The tax is not likely to gain wide support in the current Congress.

The federation is also fighting the administration and Congress on pending free-trade deals with South Korea, Colombia and Panama that are expected to boost U.S. exports by about $13 billion.

"All three free-trade agreements will cost jobs to American workers," Trumka said. "We brought in hundreds of people from around the country ... to let them know the American public says this is bad."

Although Trumka said his federation would continue to help the administration pass its $447 billion job-creation package, he took a hard line with the proposed free trade deals and suggested the AFL-CIO would use its considerable clout to fight certain lawmakers.

"We will oppose them and it will be one of the major issues when we evaluate who are our friends and who aren't our friends of working people," he said.

Democrats have traditionally relied on support from labor groups. Union contributions topped $64 million in 2010, with 93 percent going to Democrats, according to the Center for Responsive Politics.

The federation has had some success holding Democratic lawmakers accountable. During the 2010 mid-term congressional elections, the AFL-CIO tried to unseat then-Democratic Senator Blanche Lincoln and threw resources behind her challenger, Bill Halter.

In the end, Lincoln won the primary but lost to a Republican in November elections. But the federation got its point across. "We are going to support demonstrated friends of working people," Trumka said.

(Editing by Todd Eastham)