"Vavi … came down from the ninth floor … to see me in my office in a quiet area of the building. I was sitting at my desk and he came up behind me," she wrote in the Sunday Times.
"He is a big man. When I got up, he grabbed me and then kissed me. Then he locked the door. I still have the dress I wore on that day, " she said without providing more details about the incident.
Vavi released a statement earlier on Saturday in which he denied having raped his colleague.
He had been in a consensual extramarital affair with the woman. A document presented as the woman's grievance complaint of sexual harassment, Vavi's response to this, and SMSes allegedly exchanged between the two was attached to the statement.
The police could not confirm that a rape charge had been laid against him.
The mother of two said she first met Vavi at a check-in counter at OR Tambo International Airport in 2011. She helped him sort out a problem with his ticket and was allegedly told Cosatu could use "someone like me". She said Vavi took her telephone number and later offered her a job.
She said she had been hired without going through proper procedures.
"There wasn't even an interview."
While Vavi admitted to having an affair with the woman, he said she had later attempted to extort R2-million from him.
The Sunday Times quoted him as saying: “It’s a massive own goal on my part. We all do these things in dark corners and when they come out lots of people are hurt.”
“I want to apologise to everybody. It’s very sensitive, especially as it relates to my family, but I’m being blackmailed,” he said.
A Cosatu inquiry will convene on Monday following the lodging of a formal grievance by the woman. – Sapa