Billionaire activist-investor Carl Icahn gives an interview on FOX Business Network’s Neil Cavuto show in New York February 11, 2014. REUTERS/Brendan McDermid A government watchdog group, Public Citizen, said on Wednesday it will ask lawmakers to investigate whether billionaire investor Carl Icahn should have been subject to lobbying disclosure laws when he advised President Donald Trump to overhaul the U.S. biofuels program.