According to the woman, the assault took place before the March 2006 Knesset elections, while she toured the MK's home.
Ziv, 69, serves as deputy Knesset speaker and is a member of the Knesset's Economics Committee and Constitution, Law and Justice Committee. He is a widower, has three children and lives in Ramat Gan.
On Wednesday afternoon it was reported that Ziv hired Attorney Zion Amir, one of former President Moshe Katsav's lawyers in the sex offenses affair.
Talking to Ynet, Ziv said that he felt well despite the reports. "This is a political revenge and I have no doubt that the truth will be revealed," he said.
According to the report, first published in Yedioth Ahronoth, which did not mention Ziv by name, the activist accompanied the MK to his house, which had just been renovated.
When they arrived at the bedroom, he hugged her forcefully from the back, lifted her shirt, grabbed her breasts and threw her forcefully on the bed. She tried to resist, and at a certain stage managed to slip away from the house.
Two months ago, the woman told Yedioth reporter Tzvika Brot about the incident, noting that she planned to file a complaint with the police. Eventually, however, she decided not to do so.
"What happened with the Katsav affair strengthened my feeling that I should not complain," she said. "The result would be that I would be banished from society, and the person who hurt me would not be punished… I cannot expose myself now and go through the humiliation."
According to the report, a number of Knesset officials and the head of the MK's party found out about the incident. The party chairman recommended that the woman go to the police and file a complaint without delay.
Ziv denied the woman's allegations, explaining that it was political revenge.
"She can complain, that's what she usually does. But I don’t even want to refer to talk about her, because this is nonsense," he said.
A lie detector test, however, showed that the political activist was telling the truth, Yedioth reported.
The report quickly became the talk of the day at the Israeli parliament. A number of Knesset members demanded that the name of the politician who allegedly committed the offense be revealed immediately.
"We must not humiliate all 120 MKs," said MK Moshe Sharoni of the Pensioners Party.
Amnon Meranda contributed to the report