Billionaire hedge fund manager Leon Cooperman, the Chairman & CEO of Omega Advisors, said he has been sent a subpoena from the U.S. Attorney's office and the Securities and Exchange Commission, according to a CNBC report. The government is requesting more information on trades relating to various securities, Cooperman said. Cooperman told CNBC he is cooperating with the inquiry and insists his firm has acted properly. Some of Cooperman's largest holdings include AIG (AIG), Citigroup (C) and United Continental Holdings (UAL). His fund fell 2.8% last year, compared to the S&P 500's 13% rise.