Federal law enforcement agencies have launched a criminal investigation into the use of American Express cards issued by the Republican Party of Florida to elected officials and staff, according to sources familiar with the probe.

The U.S. attorney’s office in Tallahassee, the FBI and the Internal Revenue Service are all involved in the probe, which grew out of the state investigation into former House Speaker Ray Sansom. He was indicted on criminal charges that he stashed $6 million in the state budget for an airplane hangar for a friend and campaign donor.

In the federal case, Sansom and others could be charged with making false statements on their tax returns and tax evasion.

A spokeswoman for the Republican Party of Florida, Katie Gordon, said she could not confirm the investigation nor make any comments. Coming in a high-stakes election year, the investigation could expose the inner-workings of a party that has dominated state government and raked in millions of dollars from lobbyists and special interests.

(Read more: Miami Herald)