New problems for Cain - courtesy of the Koch-backed group Prosperity USA.

In a written complaint being filed today, the Center for Media and Democracy — a Madison, Wisconsin based watchdog group — charges that leaked financial records show that Block used a non profit group, called Prosperity USA, to improperly pay Cain campaign expenses. If verified, the group says Prosperity USA – which was founded by Cain’s chief of staff Mark Block — should be stripped of its tax exempt status.

“A charity founded by Mr. Block appears to have fronted tens of thousands of dollars to a political campaign that was led by Mr. Block … This requires an investigation by the IRS into the charity’s activities and expenditures,” said Lisa Graves, the executive director of the Media and Democracy Group in an eleven page letter to IRS Commissioner Douglas Shulman.

The Cain campaign did not immediately respond to a request for comment Monday morning. The campaign’s lawyer last week told NBC News that the Cain campaign takes the allegations “very seriously” and had hired an outside counsel to review the issue … The Center for Media and Democracy’s letter is the second legal complaint in four days triggered by the publication of Prosperity USA internal financial records by a blogger, Dan Bice, who writes for the Milwaukee Journal Sentinel. The IRS will investigate such complaints, but the probes – which can result in fines and a denial of tax exempt status – can often take years before they are resolved. (On Friday, the Citizens for Ethics and Responsibility filed a complaint alleging election law violations with the Federal Election Commission.)

That’s on top of the FEC problems, and the IRS violations are potentially more damaging than the FEC ones.