Federal prosecutors want to know more about efforts billionaire investor Carl Icahn may have made while he was an adviser to President Donald Trump to change the renewable fuel credits system that was costing one of his companies millions of dollars.

Icahn’s company said in a filing with the Securities and Exchange Commission last week that it had received a subpoena for records related to the federal Renewable Fuels Standard and Icahn’s role with the White House.

Icahn didn’t immediately respond to a message Wednesday. But his company said it is cooperating with the subpoena from the U.S. Attorney’s office for the Southern District of New York.

Icahn resigned from the unpaid administration job in August just before The New Yorker published a story detailing potential conflicts and even possible criminal law violations involving refining rules.

The head of the Environmental Protection Agency has said that he never promised Icahn that changes would be made to the renewable fuel credit rules.

At the time of his resignation, Icahn said he never profited from his position and that he didn’t believe the role presented any conflicts of interest. Icahn’s attorney has said Icahn didn’t exploit his relationship with Trump to make bets on renewable fuel credits.

The New Yorker magazine story highlighted Icahn’s ownership of a Texas oil refinery, CVR Energy, and the obscure rules that require refineries to blend ethanol into gasoline.

When Icahn invested in CVR in 2012, renewable fuel credits cost only about 5 cents apiece, so the company just bought the needed credits instead of investing in upgrades to blend ethanol. By 2016, the magazine reported that CVR was spending $200 million a year on the credits.

Icahn failed to persuade the Obama administration to change the point at which the ethanol blending was required, making it closer to the gas pump so refiners weren’t responsible and CVR wouldn’t have to buy the credits, the magazine wrote.

(AP)