Mehmet Oz, President Donald Trump’s nominee to lead the Centers for Medicare and Medicaid Services, may have “significantly” underpaid Social Security and Medicare taxes in recent years, according to a memo by Democratic staff on the Senate Finance Committee seen by Bloomberg News.

Dr. Mehmet Oz, the celebrity physician nominated by President Donald Trump to oversee Medicare and Medicaid, appears to have underpaid his U.S. Social Security and Medicare taxes in recent years, according to a memo by Democratic staffers on the Senate Finance Committee.

Senate Finance Committee Democratic tax staff who reviewed Mehmet Oz’s tax returns said the nominee to run the Centers for Medicare and Medicaid Services avoided paying some Medicare and Social Security taxes over three years.