Istanbul , Turkey ( CNN ) -- Turkey 's main opposition leader resigned as head of his party Monday after the circulation of a videotape allegedly showing him having an affair with a female party deputy who had once been his secretary . Deniz Baykal declared that `` there is a conspiracy against me '' and blamed the government for the video . The 71-year-old chairman of the Republican People 's Party said the secretly shot tape could not have been made without the approval of the ruling party . `` It is impossible to organize such a plot within such a short period of time without the knowledge of the ruling party , '' he said in a televised address . `` One who gives credit to unlawful and unethical plots can not defend law and ethics . '' The party is to elect a new leader at its convention May 23 and 24 . Baykal has said he would n't be a candidate , but that wo n't stop members from trying to elect him again . Numerous party members are gathering signatures from delegates to renominate him as a candidate for leadership , saying they do not believe the accusations . And Baykal said , `` My resignation does n't mean I will give in to this conspiracy or will stop the fight . '' Members of parliament wept openly during the speech by Baykal , a representative from Antalya . Afterward , Prime Minister Recep Tayyip Erdogan said he had ordered distribution of the tape halted . He added that he found Baykal 's statements `` just as ugly and worthless as the tape '' and noted that Baykal had not denied its authenticity . The resignation of the secularist party leader comes as the government is preparing to take a package of proposed constitutional changes to a national referendum . The Republican People 's Party opposes the changes . The chief prosecutor 's office in Ankara has initiated a criminal investigation , according to Turkey 's semi-official news agency Adnadolu Ajansi . CNN 's Yesim Comert and Talia Kayali contributed to this story .
Deniz Baykal blames government for allowing secret video recording . `` There is a conspiracy against me , '' Baykal says . Resignation comes ahead of referendum on constitutional changes opposed by Baykal .