Authorities, including the FBI, are investigating fake letters sent to Florida residents questioning their eligibility to vote.

FBI officials on Wednesday said they would focus on the bogus letters sent to voters in some 18 counties.

According to the Republican Party of Florida, Chairman Lenny Curry received one of the fake letters on Tuesday.

"This type of activity is not only disgusting, it is criminal, and must be prosecuted to the full extent of the law," Curry said in statement. "I call on Florida Democrats to join me in condemning this false letter writing campaign that appears to target likely voters in Florida, and help RPOF get the word out about this false campaign."

The letters raise questions about voters' citizenship status and purport to be from supervisors of election. Instead, the letters are postmarked Seattle.