Former White House aide in a new book says ex-President 's then-lawyer groped her on Jan. 6, 2021, reported Wednesday.
Hutchinson writes that Giuliani — who is 52 years older than her — put his hand "under my blazer, then my skirt" on that day, according to the report.
The alleged incident occurred behind a rally stage near the White House shortly before Trump encouraged a crowd of supporters to march to the U.S. Capitol to protest the confirmation of President 's victory over him in the Electoral College.
A spokesperson for Giuliani, 79, called Hutchinson's claim a "disgusting lie" and suggested she had invented the allegation about the former New York City mayor to boost sales of her book.
Hutchinson's memoir "Enough" is set to be published Tuesday. The Guardian obtained an advance copy of the book.
CNBC has not obtained a copy. NBC News, citing a person familiar with the book, confirmed the quotes reported by The Guardian.
Hutchinson, 27, stepped into the national spotlight last year when she gave explosive testimony to the House Select Committee that investigated events surrounding the pro-Trump riot at the Capitol that followed Trump's Jan. 6 speech.
Her new book traces her turn from Trump supporter and White House staffer to star witness in a congressional probe that recommended criminally charging the former president.
It also reportedly details, for the first time, her claim of sexual misconduct against Giuliani, who is a former top federal prosecutor.
"I find Rudy in the back of the tent" with the pro-Trump lawyer John Eastman and others, she writes. "The corners of his mouth split into a Cheshire cat smile. Waving a stack of documents, he moves towards me, like a wolf closing in on its prey."
"'We have the evidence. It's all here. We're going to pull this off,'" she says Rudy told her as he "wraps one arm around my body, closing the space that was separating us."
"I feel his stack of documents press into the small of my back. I lower my eyes and watch his free hand reach for the hem of my blazer," Hutchinson writes.
"'By the way,' he says, fingering the fabric, 'I'm loving this leather jacket on you.' His hand slips under my blazer, then my skirt," she writes.
"I feel his frozen fingers trail up my thigh," she says of Giuliani, whose eyes "look jaundiced" as he "tilts his chin up."
She said she looked toward Eastman, who "flashes a leering grin" at her.
"I fight against the tension in my muscles and recoil from Rudy's grip," Hutchinson writes.
She says that afterward, "Filled with rage, I storm through the tent" in search of Mark Meadows, Trump's chief of staff and her boss at that time.
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Giuliani's spokesperson said in a statement to CNBC that it is "fair to ask Cassidy Hutchinson why she is just now coming out with these allegations from two and a half years ago, as part of the marketing campaign for her upcoming book release."
"This is a disgusting lie against Mayor Rudy Giuliani — a man whose distinguished career in public service includes taking down the Mafia, cleaning up New York City and comforting the nation following September 11th," said the spokesperson, Ted Goodman.
In May, a former employee of Giuliani him of sexual assault in a civil complaint in New York. Giuliani "unequivocally denies the allegations" raised in that lawsuit, his spokesperson said at the time.
Charles Burnham, a lawyer for Eastman, in a statement to CNN called Hutchinson's accusations "libelous."
Eastman "does not recall ever having met Ms. Hutchinson and did not even know who she was until her public testimony before the Select Committee in the House of Representatives in June 2022," Burnham told CNN.
Attorneys for Eastman did not immediately respond to CNBC's requests for comment.
Hutchinson drew attention for her testimony in June 2022 to the Jan. 6 House committee.
She told that panel that after the rally on Jan. 6, 2021, a White House official told her that Trump had lunged at a Secret Service agent who refused to take him to the Capitol, where a mob of his supporters was swarming.
She also testified that Trump said he did not care if his supporters brought weapons to the "Stop the Steal" rally that preceded the riot.
Trump denied those details of Hutchinson's testimony.
Trump, Giuliani, Eastman and Meadows have all been charged in a sweeping racketeering case in Atlanta state court accusing them and more than a dozen others of conspiring to overturn Trump's loss in Georgia's 2020 presidential election.
They and the other 15 defendants have pleaded not guilty to charges in Fulton County Superior Court.
