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What do comedian Stephen Colbert, a Massachusetts senator and the woman trying to take his seat have in common? They are all battling super PACs, those recently legal groups that collect and spend unlimited funds from people and corporations to support or oppose political candidates.

But where Colbert used over-the-top satire to inflate the two-year-old campaign finance laws, Republican Sen. Scott Brown and his Democratic challenger, Elizabeth Warren, are employing self-imposed sanctions to diminish the influence of super PACs on their race.

Warren and Brown agreed today to shun outside groups by signing a pact to donate half the value of any ad run on their behalf by third party groups to a charity of the opposing candidate's choice.

"This is a great victory for the people of Massachusetts, and a bold statement that puts Super PACs and other third parties on notice that their interference in this race will not be tolerated," Brown said in a statement.

The Massachusetts Senate race is the first campaign of national significance in which both candidates have vowed to reject the millions of ad dollars that super PACs can provide.

"Do we know it will succeed? No," Warren said, The Associated Press reports. "But I do know that we go into this in good faith to try to have a chance to make our best case to the voters of Massachusetts. I think that's worth trying."

The Massachusetts race is expected to be the most expensive Senate race in 2012, and possibly the most costly Senate race in history.

Warren, a Democratic darling who helped the Obama administration create consumer protection regulations, is aiming to unseat Brown, whose upset victory in a special election following Ted Kennedy's death in 2010 broke the Democrats' filibuster-proof majority in the Senate.