In Florida, Virginia and Indiana, voters have received phone calls that wrongly told them there was no need to cast a ballot in person on Election Day because they could vote by phone.
In Ohio and Wisconsin, billboards in mostly low-income and minority neighbourhoods showed prisoners behind bars and warned of criminal penalties for voter fraud - an effort that voting rights groups say was designed to intimidate minority voters.
And across the United States, some employers - notably David and Charles Koch, the billionaire brothers who help fund the conservative group Americans for Prosperity - are pushing their workers to vote for Republican Mitt Romney for president.
Two weeks before what could be one of the closest presidential elections in US history, efforts to mislead, intimidate or pressure voters are an increasingly prominent part of the political landscape. Analysts say tactics typically seen in the last few days before an election are already in play.
"We've seen an uptick in deceptive and intimidating tactics designed to prevent eligible Americans from voting," said Eric Marshall of the Lawyers' Committee for Civil Rights Under Law, who manages a coalition that has a telephone hot line (1-866-OUR-VOTE) that collects tips on alleged voter intimidation.
Democrats have been more vocal in complaining about such antics. They also cite groups linked to the conservative Tea Party movement that are training tens of thousands of people to monitor polling places on November 6 for voter fraud. The controversial plan has been criticised as an attempt to delay or discourage voting.
But Republicans also have been behind some of the complaints, which have been focused largely on the eight or so politically divided swing states that are likely to decide the race between Romney and Democratic President Barack Obama.
Kurtis Killian, a Republican from St Augustine, Florida, was among those in three states who have reported receiving calls that encouraged them to vote by phone so they would not have to go to the polls.
Killian said he received a call from a man who identified himself as an employee of the Florida Division of Elections. Killian said he refused the caller's offer to cast his vote by phone then reported the call to local elections officials.
"I know there is no such thing as phone voting," Killian said. But "for someone who can't get out easily," such as elderly or disabled voters, "they might go for that - it would be convenient for them. Once you think you voted ... you won't go to the polls. My vote would be cancelled out."
Virginia's State Board of Elections received similar complaints from at least 10 people - most of them elderly - who said they had been urged to vote by phone.
Voters in Tippecanoe County, Indiana, reported similar phone calls in September, sparking an investigation by the Secretary of State's office, which oversees Indiana elections.
The probe has focused on a firm called Vote USA. It is unclear who was behind the group; its phone number is no longer active. The Secretary of State urged voters who receive a call from Vote USA to ignore it.
BILLBOARDS IN WISCONSIN, OHIO
Democratic lawmakers and activists in Wisconsin and Ohio - the most coveted of all the swing states in the presidential race because the winner there is likely to win the White House - are angry about several dozen billboard signs that have popped up in recent weeks, warning of stiff penalties for voter fraud.
The billboards were put up in mostly black and low-income communities. Most had a large picture of a judge's gavel and said "Voter Fraud is a Felony!" punishable by up to 3-1/2 years in prison and a US$10,000 fine (NZ$13,000). They were paid for by an anonymous group described only as "private family foundation."
Other billboards showed prisoners in jumpsuits peering through prison bars. Community leaders said the signs were aimed at blacks and Hispanics and the poor as well as ex-convicts - all groups that tend to vote Democratic.
City Councilwoman Phyllis Cleveland, whose district in Cleveland includes several of the billboards, said the billboards were designed to intimidate.
"I'm worried they will actually scare some of the ex-offenders, people with felony records who can vote," said Cleveland, who added that there is confusion about felons voting because it is illegal in some states. In Ohio, 12 other states and Washington, DC, felons who are not behind bars may vote.
In response to the complaints, the billboard company, Clear Channel Outdoor, said last weekend that it would take down about 140 billboards in Ohio and Wisconsin that had been scheduled to stay up until November 6 - Election Day. The company said it has a policy against putting anonymous political messages on billboards and that it erred in agreeing to the contract.
Some Ohio residents who decided to vote early to avoid long lines on Election Day said they were angry about the billboards.
A few compared them with efforts in more than 30 states to impose new voting restrictions, such as requiring voters to produce a photo ID. Several photo ID laws have been tossed aside or delayed by courts.
"There is a concerted effort to keep specific groups from the polls," said Camilo Villa, 24, who lives in the Cleveland area and voted early for Obama. "It's very concerning."
PRESSURE BY EMPLOYERS
Meanwhile, some employers have pressured workers to support certain candidates in the presidential race and other elections.
Such employers seem to be taking advantage of a 2010 Supreme Court ruling that overturned laws that banned employers from directly expressing their political opinions to their employees.
Critics of the so-called Citizens United ruling - which also led to the creation of big-money "Super PACs," or political action committees that can raise and spend unlimited amounts and have been a force in this presidential campaign - say it could make workers feel coerced into voting for certain candidates.
Several companies have sent out letters urging their employees to vote for Romney. The Koch brothers, who have given millions of dollars to back Romney and other Republicans, have come under fire for sending a "voter information packet" to 45,000 employees of Koch Industries' Georgia Pacific.
The packet, obtained by the political magazine In These Times, includes a list of candidates the company supports, with Romney at the top of the list. It also includes a letter from Koch Industries President David Robertson saying that "many of our more than 50,000 US employees and contractors may suffer the consequences" if voters elect candidates who increase regulations and hinder free trade - a presumed jab at Obama.
Some Democrats accused Georgia Pacific of trying to force workers into voting for Romney.
Lynn Rhinehart, general counsel for the AFL-CIO, the largest group of labor unions in the United States, said that employers may communicate with their workers about candidate choices, but should not link a vote with keeping their jobs.
"There could be legal issues with how it is that they are communicating with employees," Rhinehart said in a media call to discuss the election and intimidation tactics.
Georgia Pacific spokesman Greg Guest said the company's mailing was not an attempt to "intimidate" employees and that many companies and unions give members similar information.
"Unions and newspapers go further than this and actually endorse candidates to their members and readers," Guest said in a statement.
THE 'POLL CHALLENGERS'
Voting rights groups have raised concerns about volunteer "poll challengers" who will be out on Election Day to try to prevent what they see as possible voter fraud.
One group, called True the Vote, hopes to train up to one million people before November 6. Rights groups say the large numbers of monitors could be intimidating and discourage some people - particularly minorities - from voting.
"We expect organisations like True the Vote to try to intimidate people ... (by) indicating to voters, possibly Latinos, ‘You know you've got to be a documented citizen to vote,'" said Arlene Holt Baker, vice president of the AFL-CIO.
True the Vote's founder, Catherine Engelbrecht, disputed the notion that her group's election monitors might keep legitimately registered voters from casting ballots.
"We have seen no evidence about voter intimidation by TTV volunteers at the polls," she told Reuters in an e-mail.
In New Mexico, meanwhile, the state attorney general is investigating possible voter suppression after a video - secretly recorded by a group called ProgressNowNM - was circulated showing a Republican Party leader giving false information to volunteer poll monitors.
The Republican official can be heard saying that challengers could demand that voters show IDs and could prevent voters from requesting interpreters - neither of which are true. New Mexico does not require an ID to vote and interpreters are allowed. Ballots also are available in Spanish.
State Attorney General Gary King, a Democrat, said his office had received several complaints that appeared to show a "concerted effort afoot to discourage some New Mexicans from exercising their right to vote this November."