Last week, AFL-CIO President John Sweeney took to the podium at a press conference in the Rayburn House Office Building. Flanked by two of his union’s most ardent supporters in the Congress, Sen. Sherrod Brown (D-Ohio) and Rep. Phil Hare (D-Ill.), Sweeney passionately proclaimed his opposition to a free-trade agreement with Colombia.

The intensity of Sweeney’s rhetoric might have seemed out of place. After all, the entire U.S. labor movement had, just days before, scored a major victory in its fight to quash the Colombia FTA after House Democrats voted to indefinitely stall legislation on the pact.

But instead of a victory dance, Sweeney and his allies revealed an insecurity bred from years of defeats and the delicacy of their initial success on the trade deal.

“Should the Colombian free-trade agreement come up for a vote this year, we will mobilize our members and the resources of the federation to defeat it,” fumed the Bronx-born Sweeney.

While unions alone may not be able to take credit for putting the brakes on the FTA, they have been without question a key lobbying force in stymieing the agreement.

And the Colombia accord isn’t the only issue where unions are helping to thwart proposals they don’t like. The United Steelworkers and more than a dozen other labor organizations have thrown their weight against a patent reform bill that is now on hold in the Senate.

Business groups say the unions are benefiting from the politics of trade on the campaign trail; on the patent bill, they are simply one of many interests lobbying the legislation.

Still, labor movement leaders and outside observers say that unions, with their considerable political clout inside the Democratic Party, potentially are on the cusp of major policy victories.

“Right now, we see a very activist labor movement, and we see an opportunity to make progressive change so we can help the middle class,” said Leo Gerard, president of the AFL-CIO-affiliated United Steelworkers. “This is a rare moment in time when we can actually seriously consider making progress.”

Greg Denier, communications director for Change to Win, a coalition of unions that includes the Service Employees International Union and the Teamsters, said trade policy is just the beginning.

“Unions stand on the brink of the greatest revival of grass-roots organizing in the history of the United States,” said Denier, whose unions split from the AFL in 2005. “I think Colombia represents the beginning of something much larger. It is a signal that there is a shift in public opinion — not just on trade deals but across the board.”

Economist Gary Burtless, a senior fellow at the Brookings Institution who has written on labor issues, said the Colombia FTA is largely a symbolic one for the unions, who have made trade agreements a top target for more than two decades. Also, Colombia is a country with a long history of violence against union members and legal obstacles to organizing, though President Álvaro Uribe has worked to curb much of the violence.

“Unions have had a string of defeats,” Burtless said, noting the North American Free Trade Agreement, among others. “They would like to show that they still have the muscle to change the way Congress votes. It would represent for many unions a signal political achievement in showing that unions still have muscle.”

Burtless, who says he is sympathetic to many of organized labor’s goals, said the movement has been “conspicuously unsuccessful” when it comes to striking and contracts with management. “To the degree that they can exert political muscle and achieve some very public successes, it strengthens their bargaining power on a range of things,” Burtless added.

Some business lobbyists say the Colombia FTA is stalled not so much because of unions’ clout but because of the breakdown between the White House and Congressional Democrats, and the Democrats’ genuine agreement with labor’s analysis of the facts in Colombia.

Speaker Nancy Pelosi (D-Calif.) has indicated that she wants to use the FTA as leverage — perhaps to get other legislative priorities passed, such as trade adjustment assistance and children’s health care.

“We cannot allow the lives of union organizers to be used as bargaining chips for the administration’s misguided priorities, even if some good would occur from them,” Hare, a former union leader, said at the Sweeney press conference last week. “In Colombia, my fight for higher wages, better working conditions and a secure pension would have put me in grave danger.”

But Colombian Vice President Francisco Santos Calderón, who was in town late last week to lobby for the FTA, said the union message is wrong. He said he has worked for more than five years with local police officials to curb violence against unionists in Colombia.

“The unions have supported Democratic candidates in tough times, and they are cashing in on that support,” said Santos, who was once kidnapped by the Pablo Escobar Medellín drug cartel. “To a certain extent, I think they have overplayed their hand.”

Santos said the unions are using misleading information and falsehoods by saying the Colombian government has done nothing to curtail the violence against union leaders in his country.

Business advocates concede that unions are talking big. But if Democrats do win more seats in Congress and take control of the White House, they could find themselves in a plum position after this year’s elections

“I don’t think they run the show right now, but they are clearly talking with more emboldened rhetoric going forward,” said Bruce Josten, executive vice president at the U.S. Chamber of Commerce, which supports the Colombia FTA. “The ultimate prize for them is to not have a veto-wielding president.”

Denier, of Change to Win, agreed: “The 2008 election is an opportunity for the transformation of the political process and the workplace economy of the United States.”

He said unions will drive the debate on health care reform and will continue a major push for one of labor’s biggest priorities on “card check legislation,” or the Employee Free Choice Act, which would allow workers to form unions not by secret ballot but after a majority of employees sign valid authorization cards. On those issues, Denier said, Change to Win would likely work hand- in-hand with the AFL as the two have on Colombia.

“Certainly the AFL is an ally,” Denier said. “There is still one labor movement. It may have two branches, but we share the same values.”

While not a core labor issue like free trade, Gerard’s steelworkers union has worked closely on the patent bill with Corning, a large union employer. The two share lobbyist Michael Wessel of the Wessel Group.

“If the bill doesn’t come out properly, it will cost us a lot of jobs,” Gerard said.

Stan Fendley, Corning’s director of legislative and regulatory policy, said Steelworkers and Corning management have had meetings together in Senate offices. “This is one of those issues where labor and management are working together,” Fendley said. “It’s kind of rare, but it happens.”

Steve Elmendorf, a Democratic lobbyist pushing enactment of the patent bill, said that claims of union impact are overstated.

“I don’t think [unions] have had an impact on whether the bill comes to the Senate floor or not. I don’t think patent reform is a labor issue, despite the efforts of one company to make it one,” he said, referring to Corning.

Fendley said Corning brought the issue to Steelworkers’ attention, but “they make their own decisions.”

Wessel, on the other hand, thinks labor has been an important voice — along with universities, biotech companies and inventors — in debate on the bill, which would bring U.S. patent law more in line with international standards.

“Labor has been aggressive for the last several months,” Wessel said.