A woman who sought Herman Cain's help getting a job in 1997 says he was sexually inappropriate towards her, reaching under her skirt and pushing her head toward his crotch.
Sharon Bialek held a news conference with celebrity attorney Gloria Allred in Manhattan on Monday.
Bialek said the incident happened when she met with Cain in Washington to ask about getting her old job back at the National Restaurant Association. At the time, Cain was chief of the restaurant trade group.
The two were in a car for what she thought was a ride to an office building.
Bialek says when she asked Cain what he was doing, Cain said, "You want a job, right?"
The allegations have not been confirmed by NBC News. A Cain spokesman said the allegations "are completely false. Mr. Cain has never harassed anyone," the spokesman said.
"I want you, Mr Cain, to come clean -- just admit what you did, admit you were inappropriate to people," Bialek said.
Bialek said she did not file a workplace complaint against Cain at the time because she was not employed.
Bialek is the first woman to go public with accusations that Cain has engaged in inappropriate sexual behavior, and the fourth to allege misconduct.
Cain has repeatedly denied wrongdoing and has called the accusations a "smear campaign" in the week since Politico reported that two women reportedly received financial settlements from the National Restaurant Association in the 1990s after accusing Cain of sexually inappropriate behavior while they were employed there.
A third woman told The Associated Press last week that she considered filing a workplace complaint against Cain over what she deemed sexually suggestive remarks and gestures that included a private invitation to his corporate apartment.
A former pollster for the restaurant association has said he witnessed yet another episode involving a fourth woman. It was unclear whether that woman is Allred's client.The allegations have rocked Cain's unorthodox presidential campaign just as he was riding high in public opinion polls two months before the leadoff Iowa presidential caucuses.
As the new accuser surfaced, Cain was in California for what his campaign said were private events and an appearance on ABC's "Jimmy Kimmel Live!" as he works to stem the fallout of the string of allegations.
In response, Cain spokesman J.D. Gordon assailed Allred, calling her a major donor to Democrats who typically engages in self-promotion. He said the campaign would have more to say on the allegations later Monday.
Last week, Gordon predicted that Cain "could see other baseless allegations made against him as this appalling smear campaign continues."
Federal Election Commission reports show that Allred gave $1,000 to Hillary Rodham Clinton and $2,300 to Barack Obama during the 2008 presidential campaign.
Allred has a syndicated television show, "We the People With Gloria Allred," that airs on 4 New York.
Allred has represented several high-profile clients, including Amber Frey, a witness against convicted California killer Scott Peterson. Allred also represented a woman whom news reports accused of having an affair with golfer Tiger Woods.
"I consider sexual harassment the No. 1 problem in the workplace," Allred told the AP in an interview last week. "It denies equal opportunity in the workforce. If (women) don't protest it, they'll have to continue to suffer."