Federal prosecutors have issued subpoenas for information on efforts by billionaire Carl Icahn to change biofuel policy when he was an informal adviser to President Trump.

The U.S. Attorney’s office for the Southern District of New York is “seeking production of information” about Icahn’s lobbying on the Environmental Protection Agency's Renewable Fuel Standard, Bloomberg reported Wednesday. Prosecutors also want to know more about Icahn’s role as an adviser to Trump, according to a form 10-Q that Icahn Enterprises LP filed Friday with the Securities and Exchange Commission.

“We are cooperating with the request and are providing information in response to the subpoena,” Icahn Enterprises said in the filing. “The U.S. Attorney’s office has not made any claims or allegations against us or Mr. Icahn.”

Icahn resigned as special adviser to the president in August after the New Yorker published an article about the conflicts created by his advisory role.

He pressed the Trump administration to change a requirement that refiners be held responsible for ensuring that corn-based ethanol is mixed into gasoline. One of his investment firms, Icahn Enterprises, owns a large stake in an oil refinery business, CVR Energy.

Icahn unsuccessfully tried to pressure the government to change the rules regarding the "point of obligation," trying to forgive CVR and other oil refiners from the responsibility of blending the ethanol, according to the New Yorker.