Sen. Blanche Lincoln (D-Ark.) lashed out at organized labor in a new ad for having backed her Democratic primary opponent.

Lincoln, in her latest ad, targeted unions for having run ads on behalf of Arkansas Lt. Gov. Bill Halter (D), who's challenging Lincoln in a primary race from her left.

Lincoln specifically responded to an ad accusing her of not working for Arkansans.

"That ad is paid for by a bunch of Washington, D.C. unions," she says in her response. "And they're right -- I'm not working for them; I work for you."

Labor groups have pledged to support Halter in the primary race, the winner of which will likely face a tough GOP challenger this fall. Lincoln, for her part, has not enjoyed the warmest relationship with organized labor after she'd been skittish on moving forward with some elements of healthcare legislation, and had been cool toward supporting the Employee Free Choice Act (EFCA, or "card check").

Check out Lincoln's spot below: