"We'll see if Blanche Lincoln is made a better senator for having to answer to working Arkansans over these past few weeks," said SEIU political director Jon Youngdahl.
Asked whether she could bring unions back to her side, Lincoln said she always has supported workers' rights to organize.
"I've stood strong on prevailing wages and the ability to have those prevailing wages, things like that," she said in an interview Wednesday. "I'm glad to work with them, I'm glad to have their support, but if their expectations are you have to be with them 100 percent before they're going to support me, that's probably a criteria I'm not going to meet with anybody because my first and foremost responsibility and obligation is to represent the people of Arkansas."
Youngdahl also named a string of other Democrats who could see labor's wrath, including North Carolina Rep. Larry Kissell, Ohio Rep. Zach Space and New York Reps. Mike McMahon and Michael Arcuri. All voted against Obama's health care overhaul.
Space campaign manager Danny Friedman said the AFL-CIO continues to support the Ohio Democrat. [See who is giving money to Space's campaign.]
Leon Fink, a labor historian at the University of Illinois at Chicago, said the heavy investment in Arkansas shows other Democrats that labor "will bite back if necessary." But he questioned whether it was the best use of union resources.
"They turn increasingly to political campaigns when the question is whether those millions would be better put into organizing," Fink said.