The letters purport to be from county elections supervisors and question the recipient's citizenship and eligibility to vote but are postmarked from Seattle.
A statement from the head of the Tampa FBI field office, Steven E. Ibison, said the FBI will focus on letters sent to voters in 18 Central and Southwest Florida counties in the field office's region. The bogus letters have been reported in at least 23 counties.
Ibison advises any voter who receives a suspect letter should contact their county Supervisor of Elections office to verify the letter. If it's fraudulent, voters should keep the letter and contact the Tampa FBI field office at 1-866-838-1153.
The Florida Department of Law Enforcement has also opened an investigation into the bogus voter letters.