(CNN) - Lawyers representing GOP hopeful Newt Gingrich sent a letter to television stations Friday demanding they stop airing an advertisement produced by a group supporting Mitt Romney's presidential bid.
The letter claims spots created and paid for by the super PAC Restore Our Future erroneously suggest Gingrich was fined for ethics violations during his tenure as House speaker, saying, "These statements are NOT TRUE."
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The letter continues, "In fact, ANY statement, suggestion, or innuendo that Speaker Gingrich was assessed a congressional fine for violations of House Ethics Rules is fundamentally false and misleading."
Gingrich's lawyers advise the stations that airing the ad exposes them to potential civil liability.
Restore Our Future, which is supporting Romney's bid for president, produced an ad in late December that asserted Gingrich "has a ton of baggage," making him the preferred candidate for Democrats working to reelect President Barack Obama.
Among the baggage: "The fact that Gingrich was fined $300,000 for ethics violations."
Gingrich's lawyers said Friday that particular allegation was untrue.
"Any statement or suggestion of a 'fine" is false," the letter said. "Even a cursory review of either the Report itself or the Congressional Record associated with its presentation to the body of the House undeniably establish the falsity of this statement."
The letter clarified the Gingrich was asked to "reimburse the House $300,000 to offset some costs of the Committee's investigation."
Charlie Spies, treasurer of Restore Our Future, stood by the ads Friday.
"The ads run by ROF are factually correct and we will strongly defend them," Spies said. "It is understandable that Mr. Gingrich wishes that he was not the only Speaker of the House ever fined for unethical behavior, but that is his baggage and the ad will air."
Gingrich has railed against Romney's super PAC ever since they began airing negative ads leading up to Tuesday's Iowa caucuses. He has called on Romney to ask the organization to stop airing the ad, though Romney claims federal law prevents him or his campaign from coordinating with the third-party group.
Gingrich's campaign, which has said in recent days they would begin airing ads that target Romney, said Friday they are producing a spot that goes after their rival on abortion.
Gingrich Press Secretary R.C. Hammond would not offer specifics on the timing of the ad's release, but did say it would run only in South Carolina.
The ad will claim Romney allowed taxpayer dollars to fund abortions when he was governor of Massachusetts.
The Gingrich campaign's first ad going after Romney – "Bold vs. Timid" – began airing in South Carolina and New Hampshire Friday. On Thursday his campaign said it was a "significant" ad buy. Hammond said they spent $250,000 for the week in South Carolina, and $9,550 in New Hampshire. The New Hampshire ads will air around Saturday's GOP presidential debate.