Her remarks, published online by Time magazine on Wednesday, follow a tweet she posted on January 31 that said, "It's disappointing that such an iconic women's brand @Guess is still empowering Paul Marciano as their creative director #metoo." Upton used the hashtag that's come to represent the anti-harassment movement that's swept the business world.

Now, the 25-year-old is opening up about her experiences with Marciano. Upton claims that Marciano verbally harassed and touched her inappropriately starting when she was 18 years old.

Marciano denied the accusations in a statement to Time, which CNN obtained, calling them "absolutely false."

"I have never been alone with Kate Upton," Marciano said in the statement. "I have never touched her inappropriately. Nor would I ever refer to a Guess model in such a derogatory manner."

Upton claims that on her first day of shooting her first ever Guess campaign in 2010, Marciano "forcibly" grabbed her breasts, saying he wanted to make "sure they're real."

She says photographer Yu Tsai was in the room at the time of the incident, and he corroborated the claims to the magazine.

"Despite doing everything I could physically do to avoid his touch throughout the meeting, he continued to touch me in a very dominating and aggressive way," Upton said. "Grabbing my thighs, my arms to pull me closer, my shoulders to pull me closer, my neck, my breasts, and smelling me."

Upton went on to say she had two options: "Do everything I could to wiggle away and avoid his pursuit, or punch the CEO of Guess. So I decided to just wiggle away."

Yu Tsai told CNN in a statement that he is "extremely moved by the strength and courage that it has taken Kate Upton to tell her story and for the countless brave women and men who have already come forward."

Upton claims that Marciano's behavior continued for years, and that she would get fired from jobs when she denied his advances. She claims this happened on more than one occasion and recalls one instance in which she turned down Marciano's request to come to her hotel and woke up the following day to news she was fired because he said she had "gotten fat."

CNN has reached out to Upton for comment.

She told Time that Marciano's aggressive behavior continued even after she landed on the cover of the Sports Illustrated swimsuit issue. Upton said Guess Jeans offered her $400,000 in 2012 to be the face of another campaign, but she couldn't bring herself to work with Marciano again.

In its official statement to CNN with Marciano's remarks, Guess did not elaborate on Upton's decision to turn down the offer.

The supermodel says for years after Mariciano's harassment, she wanted to "quit modeling" and that she blamed herself for his behavior. But now she says she is "sick of being silenced."

"Paul used his power to make me feel insecure and powerless, but I'm not going to let him intimidate me anymore," she said. "These men think they are untouchable, but times are changing."