TALLAHASSEE —The Florida Division of Elections and state law enforcement officials are investigating reports from at least 24 counties — including Hillsborough, Pasco and Pinellas — that eligible voters have received bogus letters saying they have been flagged as suspected noncitizen voters.

The letters are written to make it look like they came from the recipient's local supervisor of elections office. The envelopes carry a similar notation. But they are not official letters and supervisors are alerting residents of the hoax.

Seemingly aimed at politically active Republicans, it's the latest case involving voter fraud to emerge in Florida and it comes less than two weeks before the Nov. 6 election.

"It makes me angry," said Jeff Guerra, a 43-year-old sales representative from New Port Richey who received a letter Tuesday. "I want this to be an honest election. Something like this is obviously a scam, I'm really taken aback."

Officials know of "dozens" of fraudulent letters, but that number could climb in the next few days, said Chris Cate, spokesman for Secretary of State Ken Detzner. The case has been referred to the Florida Department of Law Enforcement and the FBI.

"We don't know the intention of the letters," Cate said. "They certainly have the possibility of intimidating voters. … We're going to make sure the people who did this are brought to justice."

The case could be interpreted as voter intimidation, Cate said, which is a third-degree felony punishable by up to five years in jail.

Finding out more about those behind the mailing might be difficult, said Gretl Plessinger, spokeswoman for the FDLE, which launched a criminal investigation into the case Tuesday. Two weeks ago, the agency launched another criminal investigation into a case involving fraudulent voter registration applications filed by a private vendor hired by the Republican Party of Florida.

"We'll be reaching out to other states and contacting the letter recipients for the purpose of identifying commonalities," Plessinger said.

The letters arrived in envelopes with a Seattle, Wash., postmark and a date of Oct. 17. They all have the same type of letterhead, with the American flag as a backdrop to a silhouette of a bald eagle in the upper left corner. The sender swapped out the name of the supervisor of elections depending on which county they were received.

"I've never seen anybody go this far in trying to fake something from this office," said Linda Tanko, a senior elections supervisor in Orange County. "It's mean-spirited and it's causing confusion at a critical point in the election."

The recipients are similar — most are Republican, vote frequently and contribute to campaigns. Jacksonville City Council President Bill Bishop and former U.S. Ambassador John Rood each got one.

Republican Charles Callaghan of Ponte Vedra opened his letter Saturday.

"I sat there and actually had to read it a couple times because I didn't understand what it said at first," Callaghan recounted. It claimed to be from the St. Johns County elections supervisor, informing him that he may be ineligible to vote and "registering to vote under fraudulent conditions or swearing a false oath are both third-degree felonies in Florida."

Ion Sancho, Leon County's supervisor of elections, told CNN, "I suspect that whoever is sending out these letters has purchased some kind of a donor or campaign list that's given him a group of high-profile Republicans."

The letters inform recipients they have 15 days to fill out a voter eligibility form and return it to the county elections office. If they don't, they'll be removed from the voter rolls, the letter warns.

Howard Simon, executive director of the American Civil Liberties Union of Florida, blames Gov. Rick Scott's push to purge noncitizens from the voter rolls.

"The state has created a lot of confusion about citizenship and eligibility," Simon said. "No one can be reasonably surprised that people have stepped in to take advantage of the confusion."

Guerra, who said he never misses a vote and contributed $100 to John McCain's 2008 presidential bid, recently re-registered to vote and called Pasco County's Supervisor of Elections Office on Tuesday after he got his letter. They put out an alert.

By then 23 other counties had reported complaints. Brevard County on Friday was the first to contact the Division of Elections. On Monday, the state alerted all 67 counties after getting more complaints.

A coalition of voting rights advocates said they are concerned.

"Anyone responsible for this blatant attempt to tamper with the votes of Florida citizens and threaten to thwart their right to vote just days before Election Day ought to be brought to justice," said Gihan Perera, Florida New Majority's executive director.

Adam C. Smith can be reached at asmith@tampabay.com. Michael Van Sickler can be reached at mvansickler@tampabay.com.