Zwelinzima Vavi
The 26-year-old woman accused Vavi of raping her, according to a report by the Eastern Cape's Herald.
According to the newspaper, the woman filed a formal grievance to Cosatu about the incident.
In the report the woman says "Vavi "grabbed me and kissed [me], he moved to the door and locked it behind him.”
She said she asked him to stop.
"He continued to lift the dress that I was wearing and fondled my private parts.”
She said she pushed her dress down and asked him to stop again. "He did not stop, he put me on the floor and forced himself on me. The general secretary raped me.”
Vavi has maintained that the sex was consensual and has filed charges of extortion against the woman, who was reportedly asking for R2-million to keep quiet about the rape.
"I have engaged lawyers, and I am ready and willing to appear before any legitimate body to clear my name. I vehemently deny the allegations made against me by the staff member concerned," Vavi said in a statement released on the Cosatu website.
"For years now I have been dealing with consistent threats to my life, political assaults and efforts to destroy my contribution to the struggle of the working class and the poor in this country. Lately as we all know, these efforts to destroy me have intensified. I am unable not to view this matter in the same light," he said.
Vavi had also told eNCA on Thursday that he had received numerous death threats, which hinted that he could be killed in a car "accident" or through poisoning.
In his response to Cosatu's internal disciplinary probe, Vavi named the woman who laid the complaint and said that he had been having an affair with her.
He claimed that the woman was trying to blackmail him with the rape allegation, and that she had demanded R2- million in exchange for her silence on the matter.
"On July 3 2013 I received a letter … [containing] the complainant's demand for payment of R2-million rand. This letter convinced my wife and myself that I was being blackmailed to pay this amount."
The Vavis' lawyers also viewed this letter as blackmail, he said. Six days later, the lawyers sent the woman and her husband a letter "informing them that what they were trying to do is blackmail and extortion".
Vavi said there was no response to this letter. "Neither did she go to the police to lay charges."
He also responded to the allegations on Twitter.
– Additional reporting by Sapa