Houston, 8 November (Argus) — Federal investigators subpoenaed at least three companies for information on investor and former presidential adviser Carl Icahn's "activities relating to the Renewable Fuels Standard," according to corporate disclosures.

Icahn Enterprises, CVR Energy and CVR Refining were complying with inquiries by the Southern District of New York US Attorney's office, the companies said in quarterly statements.

Icahn was an outspoken critic of US biofuel blending mandates who served as what the administration described as an informal adviser on cutting regulation to President Donald Trump. He abruptly stepped down from that role in August. CVR Energy, in which Icahn holds an 82pc ownership interest, has pushed for changes to the mandates as the refiner's costs to comply with the program have climbed.