Mujahedeen-e-Khalq, usually known as the MEK, is on the U.S. State Department's list of terrorist organizations. But the group also has many prominent supporters in the United States because of its opposition to the regime in Tehran.
Rendell, who also headed the Democratic National Committee, is a recent convert, The Philadelphia Inquirer reported. But he has been an enthusiastic one, speaking on behalf of the MEK in Paris and Geneva, appearing in online videos and participating in rallies.
Now the Treasury Department's Office of Foreign Assets has subpoenaed his records on speaking fees.
Rendell refused to respond to telephone calls from the Inquirer but later left a long voice mail message with the newspaper.
"I got involved because they asked me," Rendell said. "I did extensive research and I looked at the other people who were involved and they were generals and former elected officials. I had great confidence in them."
Other supporters of the MEK include former New York Mayor Rudolph Giuliani, former FBI Director Louis Freeh, former Vermont Gov. Howard Dean and another former Pennsylvania governor, Tom Ridge, who was also the first secretary of homeland security.
Iran has accused the MEK of working with the Israeli Mossad to assassinate its nuclear scientists. The Iraqi government has ordered the MEK to leave Camp Ashraf, the base it was given 25 years ago by Saddam Hussein.