In an essay published Sunday on the online magazine Hollywood Elsewhere, Tarshis describes meeting Cosby at Universal Studios in Los Angeles in 1969 where the comedian was shooting The Bill Cosby Show.
Tarshis, who was 19 at the time, alleges that Cosby "took a liking" to her. During their visits, Tarshis says the comedian often topped her Bloody Mary cocktails with beer. On one occasion she describes losing consciousness after drinking the concoction.
"The next thing I remember was coming to on his couch while being undressed," wrote Tarshis.
"I was sickened by what was happening to me and shocked that this man I had idolized was now raping me. Of course I told no one."
'No way out'
Without coming forward, Tarshis said she "saw no way out" when Cosby asked her mother if Tarshis could come see one of his gigs. It was after this show that Tarshis alleges she woke up in Cosby's hotel suite, naked in his bed.
"It took me about 20 years to admit this to anyone," wrote Tarshis. "And though I knew I should say something, I still felt ashamed. Ashamed that I didn’t earlier."
Referring to other women making allegations against Cosby, Tarshis said "the time is right to join them."
Last week, Barbara Bowman, a former teen actress and model, published an editorial in the Washington Post claiming Cosby drugged and raped her in the 1980s.
In 2006, Cosby settled a civil lawsuit with a Canadian woman who said the comedian drugged and sexually assaulted her at his home.
The 77-year-old comedian addressed what he called the "decade-old, discredited allegations" through his attorney Sunday, who posted a message on the comedian's official website.
"The fact that they are being repeated does not make them true," wrote lawyer John P. Schmitt. "Mr. Cosby does not intend to dignify these allegations with any comment."
Cosby's upcoming appearance on CBS's Late Show with David Letterman was cancelled amid the uproar. It was originally scheduled for Wednesday. Another engagement on The Queen Latifah Show on Oct. 30 was characterized by that show as a postponement granted at Cosby's request.