The 'Elektra' star claims she was sexually assaulted by the producer in her room at the Sanderson Hotel after the BAFTA ceremony on February 10, 2008, whilst she was working as a spokeswoman for LG.
She alleges she was getting ready for bed when Weinstein started knocking on her door and she claims he implied she could get a role in a film if she had sex with him.
Natassia then claims Harvey ''forced himself on her'', saying ''it was not consensual'' and alleges ''he did not use a condom''.
After a meeting about the film, Natassia claimed she was asked to have a threesome with him and another woman. However, she declined and said a movie role wasn't worth it, leading Harvey to call her ''ungrateful''.
Natassia made the allegations when she appeared alongside her lawyer Gloria Allred at a press conference in New York City.
It comes after Harvey Weinstein - who has denied any allegations of non-consensual sex - has resigned from The Weinstein Company's board of directors, just a week after he was sacked from the company.
His brother Bob - who he co-founded the company with in 2005 - previously revealed he was also pushing for Harvey to lose his ownership interest in The Weinstein Company.
Referring to Harvey's plan to fight his firing, Bob said: ''Anybody can do what they want to do. I cannot control other people's actions. But he was fired by the board, okay? I was on that board. I fired him. He can fight. It will be a losing fight ... That is correct [that he has ownership interest in the company] and we are going to seek to sever that. It can't be done that quickly. But I am on it 24/7 and so is David Glasser and so is the board of directors that remain and so are the shareholders. This is being dealt with.''
Harvey has been accused of sexually assaulting a number of women over a 30 year period.
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