Oscar Sanchez, who was charged last week with conspiracy to commit money laundering, was ordered held without bail Monday, The Miami Herald reported.
Assistant U.S. Attorney Ron Davidson told a magistrate Sanchez was part of a "very sophisticated network."
He said Sanchez was involved in moving as much as $31 million to Havana between 2005 and 2009.
"Oscar Sanchez was a financier for fraudsters and a capitalist for the Cuban banks," prosecutors said in court papers.
Arguing against bail, prosecutors said Sanchez made 78 overseas trips in the past decade. Defense lawyer Peter Raben said most of those were to his condominium in Mexico.
The Miami area, with its large retiree population, leads the United States in Medicare fraud, investigators say. Sanchez allegedly laundered funds for at least 70 healthcare providers who defrauded the program of millions of dollars.