Donald Trump is threatening the conservative group Club for Growth with a "multi-million dollar lawsuit" for running a campaign ad that Trump's lawyer says is "the very definition of libel."

The 2016 Republican presidential frontrunner issued the cease-and-desist letter Tuesday afternoon, demanding that the group stop running their political attack ad titled "Politican." The ad, which the group launched last week in Iowa, claims that Trump supports higher taxes, national health care and the Wall Street bailout. It also features a clip of the reality television star saying he identifies "more as a Democrat" during an interview in 2004.

In a letter, which was obtained by The Washington Post, Trump's attorney Alan Garten states that the claims in the ad are "not only completely disingenuous, but replete with outright lies, false, defamatory, and destructive statements and downright fabrications."

According to CNN, Trump has voiced support for a single-payer healthcare system championed by progressives and supported a one-time 14.25 percent tax increase on the wealthiest Americans.

Still, Garten writes, "Mr. Trump does not support higher taxes."

The billionaire real estate mogul also submitted a statement to CNN, blasting Club for Growth, saying, "I am not surprised the dishonest, irrelevant and totally failing Club for Growth has resorted to attacking the definitive front runner, especially after I refused to contribute to their pathetic group. We will be releasing my current tax proposal, which is a major decrease in taxes, in the next week and will continue to expose the two faced hypocrisy of the Club for Growth and the problems groups like this perpetuate within a broken Washington, D.C."

In response, Club for Growth president David McIntosh argues that Trump has backed higher taxes "numerous times over many years." He also defended the ad, saying, "Trump's own statements prove that our ads are accurate. They will continue to run. We suggest that Donald grow up, stop whining, and try to defend his liberal record."

Watch the ad below.