The Justice Department is investigating the use of American Express cards paid for by the party, the joint Tallahassee bureau of the Herald and The St. Petersburg Times reported. The subpoena was delivered to the George H.W. Bush Republican Center in the state capital Nov. 2.
Federal prosecutors said subpoenas would never be deliberately timed to arrive on Election Day.
"We understand when we conduct an overt investigation we have to be sure and minimize the effect on an election," Assistant U.S. Attorney Karen Rhew-Miller said.
The investigation has been under way for months. The party, in its own report, blamed former Chairman Jim Greer, who was selected by Gov. Charlie Crist. Crist left the party when he realized he would lose the senatorial primary to Marco Rubio, ran as an independent and was defeated.