Mr Cain has dismissed the allegations as a smear campaign designed to spoil his rise to the top of the polls.
The former business man said there was “not an ounce of truth” to the allegations and the graphic, televised account from the latest woman to come forward, Sharon Bialek, was “totally fabricated.”
Mr Cain is set to answer reporters’ questions on the issue, reversing course after saying on Saturday that he had finished talking about the claims of sexual harassment that first became public with the airing of anonymous complaints by two other women more than a week ago.
Ms Bialek went on television on Monday and became the fourth woman to accuse Mr Cain, and the first to go public. She claimed Mr Cain groped her in a car after she asked for his help finding a job.
Mr Cain, a novice politician and surprise entrant into the presidential race, has risen to the top of public opinion polls and emerged as the main conservative challenger to Mitt Romney. Tea party activists and conservatives unready to support the former Massachusetts governor have flocked to Mr Cain’s style and self-styled outsider image in recent weeks.
There are, however, growing signs of unease in conservative circles after, one by one, a handful of women claimed Mr Cain acted inappropriately toward them while the head of the National Restaurant Association in the 1990s.
At least two women who worked at the restaurant group under Mr Cain filed sexual harassment complaints and received payouts to leave the association.
A third woman said she considered making a workplace complaint against Mr Cain over what she deemed sexually suggestive remarks and gestures that included a private invitation to his corporate apartment. And a former pollster for the restaurant association has said he witnessed yet another episode involving a different woman.