Gary Johnson of the Libertarian Party and Virgil Goode of the Constitution Party could have an impact on who wins the election, CNN reported.
Together, they are in a position to siphon a few thousand votes from Romney and perhaps Obama in some of the handful of battleground states considered up for grabs and therefore decisive in determining the winner, it said.
Goode, a former Democrat-turned-Republican Congressman from Virginia, is known for his anti-immigration stance and other strongly conservative policies.
He routinely won well over 120,000 votes in his home district in elections from 1996 to 2008 and if he secures only 10 per cent of that support this time, it could be enough to swing what is currently considered a dead-even race for Virginia's 13 electoral votes to Obama.
"Virgil Goode is a wild card, particularly in Virginia," Stuart Rothenberg of the Rothenberg Political Report was quoted as saying by CNN. "He could be a factor even if he wins only a handful of votes."
On Johnson, Wendy Schiller, a political science professor at Brown University, said a similar scenario involves the former Republican governor of New Mexico in other states considered too close to call like Colorado, Nevada and New Hampshire.
The three states, with a combined 19 electoral votes, are known for independent-minded voters, enough of whom might be inclined to back a Libertarian instead of Romney, she said.
A CNN/ORC International poll in Nevada last month showed Goode winning 4 per cent support and Johnson 3 per cent, with Obama holding a 47 per cent-44 per cent lead over Romney there.
Downplaying the impact of "third-party" candidates, Republican National Committee Chairman Reince Priebus recently told CNN that Johnson's candidature was "almost a non-factor."
Voters "are not going to throw their vote away when we have an election here that's about the future of America," Priebus said. "I don't see that happening."
Scott Rasmussen, president of the polling company Rasmussen Reports, was quoted as saying that "If the race is close enough, 100 votes can matter."
According to CNN, Goode rejects any insinuation that he seeks to play a spoiler role, claiming that his policies would be better for the country than those of Obama or Romney.
Johnson depicts himself as more liberal than Obama on social issues and more conservative than Romney on fiscal issues, the report said.
