Democratic Rep. Daniel Lipinski wants the Internal Revenue Service to investigate the Illinois Policy Institute, a conservative think tank. 

Lipinski sent a letter asking the IRS to explore whether CEO John Tillman used money from the institute to benefit for-profit companies, according to ProPublica.

“Federal law provides tax benefits that help nonprofits pursue their agendas, including ideological agendas,” Lipinski wrote in a letter to acting Commissioner David Kautter. “What it does not allow, however, is for an individual to use a non-profit organization to inure excessive benefits to himself. I fear that is exactly what Mr. Tillman has done.”

Tillman previously defended the dealings.

“Obviously, these are all fully disclosed transactions, all at fair market value as they should be,” he said.

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One of the deals in question was a zero-interest loan worth $49,400 from Think Freely Media, one of Tillman’s nonprofits, to Crowdskout, a for-profit company he controlled.

“This appears to be to be an attempt by Mr. Tillman to derive a private benefit from Think Freely Media’s ostensibly charitable activities,” Lipinski wrote.

In addition, Think Freely Media gave grants to nonprofits that used Crowdskout. Lipinski’s call for investigation come after ProPublica published an investigation with the Chicago Sun-Times.

Lipinski, a member of the conservative Blue Dog Coalition, is facing a primary challenge from Marie Newman in Illinois 3rd District.

In the past, Lipinski has been criticized for voting against the 2010 health care law and opposing abortion rights. 

Illinois’ primary is on March 20.