Last month, the AFL-CIO endorsed Obama, quieting all the talk about any rift or lingering differences between the President and organized labor. Many Dems hope enthusiastic union support will help Obama limit losses among blue collar whites in the swing states — something that could prove decisive in the 2012 election.

Those hopes may have hit another snag: That rift has cracked open a bit once again.

In an interview just now, AFL-CIO president Richard Trumka ripped into Obama for taking a key step this weekend towards the U.S.-Colombia Free Trade Agreement — which Trumka claimed would have domestic political ramifications for Obama. Trumka said continuing betrayal of labor would make it harder to turn out supporters this fall and was already muddying Obama’s efforts to draw a sharp contrast with Mitt Romney over who represents the 99 percent.

“The more these things happen, where workers interests are subjugated to other interests, it has a cumulative effect, making it harder for us to energize our members and get them out in the numbers necessary in the fall,” Trumka told me.

“The candidates have to decide whether they represent the 99 percent or the one percent,” Trumka continued. “Each time this happens, it obscures the clearness with which the president represents the 99 percent.”

The blast at Obama is Trumka’s most direct criticism of the president yet on the issue. This weekend, Obama certified Colombia’s labor protection efforts, clearing the way for the free trade deal to take effect on May 15th. Previously, Trumka had warned the President that certification was premature, because Colombia had failed to do enough to stop the killing of union backers and human rights workers, and because the deal risks harming American workers while enriching multinational corporations

Trumka suggested that labor leaders had expected the White House would give them a little more time to improve the deal, and that they had been surprised by the sudden approval. Pressed on whether the move could really hurt enthusiasm among blue collar swing voters, Trumka insisted that the labor organizers on the ground who will drive turnout were already responding negatively.

“The people on the ground who deliver the votes are...wondering why,” Trumka said. “Our job is made more difficult.”