Sen. Blanche Lincoln (D-Ark.) said Sunday that big labor unions and the liberal group MoveOn are making her runoff against Lt. Gov. Bill Halter (D) close.

Lincoln and Halter will face one another for the Democratic Senate nomination in the Natural State on Tuesday, and outside liberal groups have invested much time and money into defeating Lincoln, whom they see as too far to the right.

"Well we have had great support, but to be honest with you Candy, the D.C. unions have put about $10 million in this race in the last 12 weeks and that's just on the TV," she said on CNN's "State of the Union" program. "They have also inundated Arkansas with outside workers that they have bust in to go door-to-door. They have done some ugly mailers in the mail and they have radio ads, a whole host of other things."

In her campaign, Lincoln has sought to paint herself as a centrist who is in tune with what voters want and Halter as a proxy for national outside groups she says are outside the mainstream.

She claimed that 60 percent of Halter's campaign war chest came from MoveOn and that more of his donors are from California and not Arkansas. Last month, the AFL-CIO said it would aggressively campaign for Halter.

But she failed to muster a majority of the vote in the Democratic primary against Halter and others several weeks ago, setting the stage for this week's runoff. Still, she remained confident that she would beat Halter on Tuesday.

Many expect Lincoln to have a tough time defeating Halter in an electoral that is tilted against incumbents. Two sitting senators, Bob Bennett (R-Utah) and Arlen Specter (D-Pa.) have already been denied another term in primary races.

Also on CNN, Halter downplayed his support from unions, saying that he will fight for the middle-class in Arkansas, which is not a heavily unionized state, if elected. 

"Yeah, I understand the point that's being made, but frankly Candy I think it's a diversion from the real issue," he said. "The real issue here in this race is who's going to stand up for middle class Arkansas families."