New Hampshire Gov. Maggie Hassan (D.) has said she will fight super PACs and money in politics as part of her bid for the U.S. Senate, but balked at an opportunity to cut down on special interest money during the 2016 campaign.

Hassan’s rival, freshman Sen. Kelly Ayotte (R., N.H.) signed a so-called "People’s Pledge" promising to donate money to charity every time a third party organization, such as an interest group’s super PAC, airs an advertisement attacking Hassan.

"In the event that a third party organization airs any broadcast … that promotes or supports a … Candidate, that Candidate’s campaign shall, within three (3) days of discovery of advertisement buy’s total cost, duration, and source, pay 50% of the cost of that advertising buy to a charity of the opposed Candidate’s choice," the pledge says.

Ayotte sent a letter inviting Hassan to sign the pledge on Thursday, saying that Hassan and her supporters "have falsely accused me of standing with" special interest groups.

"We owe it to the people of New Hampshire to have an honest discussion of our respective records and stand behind the ads run on our behalf. But excessive spending by third party special interest groups threatens to drown out New Hampshire voices in our race and undermine the meaningful debate that our citizens expect and deserve," Ayotte said in the letter. "Campaigns don’t have to be driven by third party groups—we can change the status quo and take a stand to say this race should be about New Hampshire."

Hassan did not return a request for comment from the Washington Free Beacon.

The Ayotte campaign said that Hassan’s refusal to immediately sign the pledge amounted to hypocrisy. The Democrat has vowed to repeal the Citizens United decision, which allowed for the creation of super PACs and struck down campaign spending restrictions as an unconstitutional violation of free speech rights. Hassan has made fighting against special interests a central theme of her campaign, even as she attended fundraisers with a lobbyist for the libertarian Koch Brothers.

"Washington has given in to powerful special interests and lobbyists who rig the system for themselves and against the middle-class, and I believe we can do better for New Hampshire families," Hassan said in a statement as she launched her campaign.

Ayotte campaign manager Jon Kohan said in a press release that Hassan should sign the pledge to prove that her criticism of special interest groups is not merely rhetoric.

"It's disappointing that Governor Hassan's first reaction to the People's Pledge wasn't to sign it—but rather to launch more ugly attacks," Kohan said. "Since her very first day in the race, Hassan has repeatedly railed against third party special interest groups. If Governor Hassan means what she says and this isn’t just a campaign talking point, she’ll immediately join Kelly by signing the pledge to keep third party special interests out of this race."