In a possible close election people are anxious about every single vote and watchdogs are already monitoring possible voter fraud, large or small, in the early votes. Abc's senior justice... See More
In a possible close election people are anxious about every single vote and watchdogs are already monitoring possible voter fraud, large or small, in the early votes. Abc's senior justice correspondent pierre thomas reports tonight on what some critics are calling voter intimidation. Reporter: Travis horn of tampa, florida, is angry. You've served in the military, try to be a good citizen and then to get this letter, it's a little insulting. Reporter: Horn was one of dozens of republicans in 28 counties in florida who got this letter in the mail questioning whether they were citizens. Sharon calvert got one too. It says that there's a question on you eligibility to vote. And if you don't provide certain information and documentation within 15 days you'll be thrown off the rolls. Reporter: The letter, which claimed to be from county election officials, warned that voter fraud is a felony. The fbi has launched a voter intimidation investigation into a political dirty trick. Take it down now. Reporter: In ohio and wisconsin billboards like these started popping up mainly in minority communities, warning voter fraud is a felony. This billboard is nothing but a symbol of pure, unadulterated voter suppression to target an african-american community. Reporter: After the controversy exploded, the billboards came down but tension remains. But as the election approaches the most likely legal battles will involve access to the polls. Let people vote. Reporter: On sunday this crowd became outrages when the polls were temporarily closed in palm beach after they stood in line for hours. Expect lawyers to sue to keep the polls open if there overwhelming turnout. Diane, thousands of lawyers will fan out across the country looking for any hint of problem. If this is close, there will be a fight for every te. I know you'll be stand di sentri tomorrow night.
This transcript has been automatically generated and may not be 100% accurate.