(FOX News) - With Election Day polls set to open in mere hours, those monitoring the vote for fraud and funny business are already on high alert.
Late last month, the state of Florida raised flags after strange letters started to go out telling voters that their citizenship was being questioned and that voting could expose them to possible jail time.
Then in Ohio, Nevada and other battlegrounds, reports surfaced of voters trying to make their choice for president on touch-screen machines only to see the machine register a different candidate. Typically, they voted for Mitt Romney and the machine marked President Obama.
Among the latest allegations is that NAACP workers showed up at a polling site in Houston "electioneering" for Obama and refused to leave -- though the NAACP adamantly denies it.
The incident was detailed by a poll watcher for the group True the Vote. In a written statement, monitor Eve Rockford claimed NAACP representatives arrived at the Houston site Friday afternoon "with probably 50 cases of bottled water" and began handing them out to voters.
"They were talking to them about flying to Ohio to promote Barack Obama. They were stirring the crowd," Rockford said.
Bill Ouren, national elections director with True the Vote, told FoxNews.com this constitutes "electioneering discussion inside the polls," which is against Texas law. Electioneering is not allowed within 100 feet of a polling site.
Rockford said that the NAACP representatives also were moving people to the front of the line, angering others at the polling site. But she said the judges on site were unable to stop them. "The NAACP basically ran this poll location and the judges did nothing about it," she said.
Ouren said the judges did ask the NAACP representatives at one point to turn their NAACP shirts inside-out. They initially refused but eventually complied, he said.
But Gary Bledsoe, president of the Texas NAACP, challenged virtually every one of those claims.
"The NAACP folks didn't do anything at all that was wrong," he told FoxNews.com. Bledsoe said the representatives were merely helping move elderly and disabled residents who were standing outside in the heat to the inside of the building. "They did not cut them in line," he said.
Further, Bledsoe said nobody with the state NAACP discussed going to help Obama -- because "they're going to be here on Election Day. They're not going to Ohio."
Sgt. Grady Castleberry with the local sheriff's department backed up Bledsoe, saying he was there and never heard them say anything about either candidate. He said somebody else on the site not affiliated with the NAACP, though, was potentially giving inappropriate advice by urging people to vote "straight ticket." Castleberry said the issue at the polling site was not the NAACP at all, but how elderly and disabled voters were being treated.
Harris County Clerk Stan Stanart, though, told FoxNews.com the NAACP representatives "were in there illegally" despite their intentions. He also acknowledged that the election judges on site didn't "really take control."
There are reports elsewhere of potential voter fraud and other irregularities.
In Iowa, officials have opened a voter registration and absentee ballot investigation that reports say involves complaints about Democratic campaign workers and allegations of false signatures.
The Republican National Committee claims "it appears to be illegal activity involving Democratic and Obama campaign operatives engaged in absentee ballot canvassing."
One man says this happened to his 75-year-old mother.
Iowa Secretary of State Matt Schultz, a Republican, is investigating, and a spokesman told Fox News "we take all allegations of voter fraud seriously -- that is why we have hired a Department of Criminal Investigation investigator to handle all of the allegations of voter fraud in Iowa.
The Iowa Democratic Party has not returned requests for comment.
Meanwhile, in Oregon, there is a ballot-tampering investigation. Reports say a county clerk may have filled in the names of Republican candidates that voters left blank. And outside Cincinnati, there are concerns that voters registered at a vacant lot could be used for voter-fraud purposes. Eighteen people are registered to vote there, even though the trailer park that was once there was removed three years ago.
The Ohio Voter Integrity Project is challenging the names to prevent possible voter fraud.
"It makes me feel angry, that somebody hasn't done anything about this," said Denise Mayer, of the Ohio Voter Integrity Project. "And the more that we bring it to people's attention, the more they want to talk about disenfranchising the voter, which is ridiculous."
Ohio elections officials say they will be on the look-out for any possible fraud or election problems.
"If they see some untoward activity taking place, there's going to be a polling location coordinator there," said Jeff Hastings, director of the Cuyahoga County Board of Elections in Ohio. "They can advise that person who's responsible for making sure that doesn't happen there. Obviously if they see anything else they can call our board and law enforcement."
And in Las Vegas, a woman -- a registered Republican -- has been charged with trying to vote twice.
Perhaps the most memorable incident of voter intimidation -- or at least the most controversial -- from the 2008 election was the appearance by New Black Panther Party members at a Philadelphia polling site. One of them was holding a billy club -- it resulted in a federal case, though the local leaders faced no serious punishment.
According to the Philadelphia Daily News, New Black Panthers leader Malik Zulu Shabazz has said the group will "consider" whether to monitor polling places again this year. Shabazz said on WABC Radio that the group wants to watch for "intimidation against our people," but said nobody will have any weapons on them this time.
FoxNews.com's Judson Berger and Fox News' Eric Shawn contributed to this report.