Democrats are criticizing Wisconsin U.S. Senate hopeful Tommy Thompson over published reports indicating his involvement with a bill pending in the North Carolina legislature.

Bloomberg Businessweek reported that Thompson was one of four national GOP luminaries to contact North Carolina House Speaker Thom Tillis (R-Charlotte) regarding a bill covering new regulations for dental-management companies. Thompson, a former U.S. health and human services secretary, along with former Florida Gov. Jeb Bush, former U.S. Senate Majority Leader Bill Frist and former Mississippi Gov. Haley Barbour contacted Tillis about the bill, which has been opposed by private equity companies, Bloomberg BusinessWeek reported.

“It’s not terribly common to have these types of names” intervening on a state bill, said Jordan Shaw, a spokesman for Tillis.

Their interest marks the Tar Heel State as the front line in a national struggle over dental management companies. Fueled by Wall Street money, at least six such firms are under scrutiny by two U.S. senators and authorities in five states over allegations that they soak taxpayers through excessive Medicaid billings, abuse patients via needless treatments and run afoul of laws that say only licensed dentists can practice dentistry.

The North Carolina bill would place new strictures on such companies, which have become a favored investment of the private equity industry. Private equity firms have bought or put money into at least 25 dental-management companies in the last decade.

Thompson is competing against former Rep. Mark Neumann, Jeff Fitzgerald, speaker of the state assembly, and businessman Eric Hovade for the Republican Senate nomination and the right to face Democratic Rep. Tammy Baldwin in the November election.

A former Wisconsin governor, Thompson is a partner in a New York private equity firm specializing in the health care sector and a former partner in a Washington law firm specializing in the health care industry. In recent weeks he has come under scrutiny for his acceptance of a board chairmanship at a Florida pharmaceutical company, a post he accepted after saying he was not taking on more corporate board seats. Thompson has served on more than 20 corporate boards since leaving the U.S. Department of Health and Human Services in 2005.

Thompson's spokesman told the Milwaukee Journal-Sentinel that he did not contact Tillis to lobby but rather to learn about the bill.

"He has not formed a position on the legislation and he has no financial stake it in," Thompson spokesman Brian Nemoir told the Journal-Sentinel.

Democrats think differently.

“If Wisconsinites needed anymore [sic] proof that Washington insider Tommy Thompson [is] trying to hide the fact he is a Washington insider who is more interested shilling for special interests on Wall Street than fighting for Wisconsin taxpayers, here it is,” Democratic Senatorial Campaign Committee spokesman Matt Canter said in a written statement. “Tommy Thompson was caught red-handed trying to protect Wall Street special interests that have paid him millions and then misled Wisconsinites about what he was doing."

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