MPs began to debate a resolution, drafted by the opposition Islamists, accusing Mrs Ciller and her businessman husband of having meddled in the sale of state-owned shares in carmaker TOFAS during her recent tenure as prime minister.
"Corruption was mixed into it, as Tansu Ciller opened the sealed tender offers - something she was not authorised to do - without the presence of any members of the [privatisation] commission," said the resolution, read aloud as the debate opened.
"The Privatisation Administration did not award the shares to those with the best price but to two separate consortia known to be close associates of the Cillers," it said.
Mrs Ciller, a US-educated technocrat, has dismissed the charges as politically driven. Throughout the corruption row, the prime minister Mesut Yilmaz has resolutely refused to defend his partner, Mrs Ciller, leaving MPs from his Motherland Party (ANAP) free to vote as they choose.
He and most of his MPs are expected to vote for a parliamentary investigation into the TOFAS sale. Separate corruption charges against Mrs Ciller were referred to a commission late last month.
Either inquiry could lead to Mrs Ciller's impeachment by the Supreme Court, effectively killing off her bid to regain the premiership next January, as scheduled under the coalition deal.
"The beans have been spilled. The plan is to send Ciller to the Supreme Court and prevent her from becoming prime minister," Turkey's first woman leader told women activists from her True Path Party ahead of the vote.
Mrs Ciller also warned that, should her coalition fall apart, overwhelmingly Muslim but secularist Turkey would see the Islamic Welfare Party poised for power.
The normally reserved Mr Yilmaz returned to his campaign attacks on his rival-turned-partner. "Mrs Ciller . . has no right to blame anyone else. Trying to divert attention cannot detract from the seriousness of the allegations."
A commission was set up last month to study whether contracts with state-owned electricity company TEDAS were manipulated to benefit the Cillers and their associates.
Mr Yilmaz and Mrs Ciller, bitter rivals despite a shared pro-market vision, were forced to form a coalition in March, after inconclusive elections.Reuse content