Novelist Zinzi Clemmons confronted Diaz at a literary festival in Australia, before publicly accusing him of forcibly kissing her six years ago while she was a 26-year-old graduate student at Columbia University.
Clemmons says the incident happened after she invited the Pulitzer winner to speak at a workshop while she was attending the Ivy League school.
"He used it as an opportunity to corner and forcibly kiss me," she tweeted. "I'm far from the only one he's done this 2, I refuse to be silent anymore."
Short story author Carmen Maria Machado and novelist Monica Byrne have also taken to Twitter to accuse the Dominican-born novelist and university professor of being verbally aggressive.
In April, Diaz published a searing essay in The New Yorker revealing that he had been raped as an eight-year-old.
He narrated its damaging impact on his life, detailing depression, drinking and infidelity.
"I take responsibility for my past," Diaz said in a statement to The New York Times via his literary agent in reference to the women's accusations.
"That is the reason I made the decision to tell the truth of my rape and its damaging aftermath. This conversation is important and must continue.
"I am listening to and learning from women's stories in this essential and overdue cultural movement. We must continue to teach all men about consent and boundaries," he said.
The Pulitzer Prize Board said Thursday it had ordered an "independent review" into allegations of misconduct against Diaz, and that while he had asked to step down as chairman, he would remain on the board.
"Mr Diaz said he welcomed the review and would cooperate fully," it said in a statement. Diaz had been elected incoming chairman only last month.
Washington Post columnist Eugene Robinson, the board's immediate past chairman, will take over on an interim basis.
A string of powerful men have been publicly accused of sexual misconduct and lost their positions in the #MeToo cultural watershed sparked by the downfall of Hollywood producer Harvey Weinstein and Kevin Spacey last year.
Born in the Dominican Republic and raised in New Jersey, Diaz won the Pulitzer Prize in 2008 for The Brief and Wondrous Life of Oscar Wao.
He is a writing professor at the Massachusetts Institute of Technology.
