Sen.  Tammy Duckworth (D-Ill.) is asking the Federal Bureau of Investigation, “in carrying out the FBI's priority of combating major white-collar crime and public corruption at all levels,” initiate a criminal investigation into the activities of Carl Icahn and “his potential violations of Federal law and fraudulent activity tied to the Federal Renewable Fuel Standard program.”

On Aug. 18, Icahn, a billionaire investor and legendary corporate raider, resigned from his role as a special advisor to President Donald Trump. “This will confirm our conversation today in which we agreed that I would cease to act as special advisor to the President on issues relating to regulatory reform,” he wrote.

“Contrary to the insinuations of a handful of your Democratic critics, I never had access to nonpublic information or profited from my position, nor do I believe that my role presented conflicts of interest,” he added in his resignation letter to President Trump. “Indeed, out of an abundance of caution, the only issues I ever discussed with you were broad matters of policy affecting the refining industry. I never sought any special benefit for any company with which I have been involved, and have only expressed views that I believed would benefit the refining industry as a whole.”

The resignation coincided with an article published in the New Yorker regarding conflicts of interest and Icahn’s efforts to parlay his unofficial White House post to personal gain. Critics, including those cited in the article, have cited Icahn’s stake in the Texas refiner CVR Energy as an example of how his influence at federal agencies, including the Environmental Protection Agency, could be a boon to his companies’ bottom lines.

Duckworth suggests, in her letter to the FBI, that Icahn potentially violated the principal criminal conflict of interest statute. Section 208 of Title 18 of the United States Code. It prohibits officers or employees of the Executive Branch from participating personally and substantially in a particular government matter that will affect their own financial interests.

“Mr. Icahn appears to have abused his role as a special advisor to the President of the United States on issues relating to regulatory reform by participating personally and substantially, through recommendation and the rendering of advice, on a government matter that directly affects his own financial interests,” she wrote. “Specifically, his efforts advising and recommending that President Trump direct the EPA to move the point of obligation under the RFS program constituted his personal and substantial involvement in a particular government matter in which [he] had a direct financial interest as the Chairman of the Board of Directors of CVR Energy.”

Icahn also controls 82 percent of CVR Energy. As a refiner, CVR the company is an obligated party under the Federal RFS program and must comply with the law by making sure a certain amount of renewable fuel is blended into their product or purchasing renewable identification numbers (RINs) credits, the "currency" of the RFS program that may be purchased to comply with the program in lieu of blending renewable fuels into their products.

“Our nation relies on the FBI to combat major white collar crime and public corruption that undermines public trust in government,” Duckworth wrote. “It would set a dangerous precedent for the FBI to turn a blind eye to suspicious activity that was so flagrant.”