A Harvard professor who operates a Super PAC unfairly labeled New Hampshire U.S. senate candidate Scott Brown a lobbyist in a campaign mailer, Brown’s campaign manager claims in a “cease and desist” letter.

“Your MAYDAY Super PAC has issued a piece of mail to New Hampshire voters falsely calling Scott Brown a ‘Washington lobbyist.’ This is a flat-out lie,” wrote Brown campaign manager Colin Reed in a letter to Lawrence Lessig, an ethics professor at the Ivy League school.

Lessig claims to have started MAYDAY, which has been dubbed “the Super PAC to end all Super PACs,” in order to limit money in politics.

MAYDAY is supporting Jim Rubens against Brown in Tuesday’s Republican primary, calling him the only Republican in the U.S. “committed to fixing the corrupt campaign finance system.”

In its mailer, MAYDAY calls Brown a “Washington insider” and a “Former Washington lobbyist.” Last year, Brown, a former Massachusetts U.S. senator, began working as counsel for Nixon Peabody, a “law and lobby firm.”

Reed denies the mailer’s main claim.

“Scott Brown is not nor has he ever been a lobbyist. Ever,” Reed wrote in the letter to Lessig.

“We call on you to immediately cease and desist with the mailer in question, and to use one of your various media appearances as a purported authority on ethics to retract your falsehood,” Reed wrote, adding that the campaign is leaving their “legal options on the table.”

Reed also called Lessig a “hypocrite,” given his field of study and the stated goals of his Super PAC. (RELATED: RICH Leftists Fund Harvard Prof’s Anti-Big Money Super PAC)

“Using the veneer of Harvard University and your position as the Faculty Director of Harvard’s Center for Ethics to lend you credibility, you have turned your Super PAC – which you publicly stated was formed to fight the existence of Super PACs – into just one more negative message machine that exists to launch unethical and untrue attacks,” Reed wrote.

Lessig responded to Reed at his blog, admitting that Brown was not technically a lobbyist, while claiming that he functioned as one.

“So yes, according to the Senate, Scott Brown isn’t a ‘lobbyist,’” Lessig wrote. “But I submit to anyone else in the world, a former Senator joining a ‘law and lobbying firm’ to help with Wall St’s ‘business and governmental affairs’ is to make him a lobbyist.”

Brown is considered the GOP primary favorite. The winner of the race will face Democratic incumbent Jeanne Shaheen.

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