Federal investigators are probing Carl Icahn's advisory role to President Donald Trump's White House.

His investment firm, Icahn Enterprises L.P., revealed in a financial filing that the government had subpoenaed information relating to the firm and Icahn's activities relating to federal biofuel policy.

Icahn quit his role with the Trump in administration in August, right around the time The New Yorker published a story suggesting Icahn could be in legal jeopardy for using his role to influence regulations that would benefit his firm's investments.

Back in August, Carl Icahn quit his role advising President Donald Trump's administration — right around the time The New Yorker reported he could be in legal jeopardy for his attempts to change biofuel policy that would benefit his investments.

Now, the feds are investigating Icahn's informal advisory role to the Trump administration in connection with his investment firm, Icahn Enterprises L.P., which has a significant stake in a fuel refiner that would benefit from regulatory changes that Icahn reportedly lobbied for.

In a filing with the Securities and Exchange Commission, Icahn Enterprises announced the US Attorney's office for the Southern District of New York had issued a subpoena seeking information related to the firm and Icahn's activities while he was an advisor to Trump:

"The U.S. Attorney’s office for the Southern District of New York recently contacted Icahn Enterprises L.P. seeking production of information pertaining to our and Mr. Icahn’s activities relating to the Renewable Fuels Standard and Mr. Icahn’s role as an advisor to the President. We are cooperating with the request and are providing information in response to the subpoena. The U.S. Attorney’s office has not made any claims or allegations against us or Mr. Icahn. We maintain a strong compliance program and, while no assurances can be made, we do not believe this inquiry will have a material impact on our business, financial condition, results of operations or cash flows."

How did Icahn wind up in the sights of federal investigators?

Here's a rundown of some key takeaways from Patrick Radden Keefe's August profile in The New Yorker that details Icahn's attempts to change the Renewable Fuels Standard: