Police opened an investigation Tuesday into a vote-buying scheme that Labor leader Shelly Yacimovich says involves the party's former chairman, Amir Peretz and two other Labor party members.

Peretz, a former defense minister who is now a Knesset member for the Hatnuah party, was first incriminated by a Labor source close to failed Knesset contender Sami Shoshan, who told the Yedioth Ahronot daily that Peretz, MK Erel Margalit (Labor) and a former Labor MK whose identity has not been verified by Haaretz were either involved in or witnesses to the payment of "vote contractors" who solicited votes for a candidate or group of candidates in the party primary in November.

Peretz has denied involvement in the reported vote-buying scheme.

Referring to Tuesday's Yedioth article, a spokesman for Peretz said, "All the details described in the report are fabricated from whole cloth and have no connection to reality."

Sources in Peretz's office said he found out about the issue only when a reporter called him Monday night. They said they knew nothing about the investigation and called Yacimovich's comments "irresponsible."

Margalit maintained he had nothing to do with the scheme as well.

"I would like to clarify that I have never paid or given anything to anyone in exchange for votes," he wrote on his Facebook page, suggesting that someone was trying to tarnish his reputation.

Police Commissioner Yohanan Danino on Tuesday confirmed launching a probe after receiving intelligence on the scheme, and vowed to get to the bottom of the allegations.

"The police will not be a pawn in the hands of any political body," he said. "They will work tirelessly to uncover the truth."

Danino noted that in recent weeks he has been dealing with a multitude of complaints over the integrity of several parties with regard to the elections.

A source cited in Yedioth's report passed a polygraph test before the story was publishd.

"I was next to him at various times when he handed over money in exchange for support for his political deal," the source close to Shoshan was quoted as saying about a candidate who went unnamed in the report. "We met with vote contractors in cafes and restaurants, and after each meeting he sent me to bring the checkbook from the car. In many instances I witnessed payment in exchange for support at the polls."

Amram Mitzna, another former Labor chairman who is now an MK for Hatnuah, called on Peretz and others implicated in the scandal to suspend themselves from office if they are indicted.

Although the original Yedioth report did not reveal Peretz's name, or even that of the party involved, Yacimovich did so in a radio interview Tuesday morning.

"I know that, very unfortunately, this happened in the Labor Party," she told Army Radio. "I know that the former senior minister [alluded to in the report] is Amir Peretz." She said the party "harshly condemns" the purchase of votes.

Some Labor members criticized Yacimovich for publicly pointing the finger at her predecessor, who is no longer a member of the party, and failing to mention other Labor politicians implicated in the vote-buying scheme.

"Three others involved in the affair, including a sitting MK, are members of the Labor Party," one critic said. "Yacimovich attacked Peretz because he's an easy target – he's her direct rival – but she's playing down the fact that there are suspicions of corruption within the Labor Party. Yacimovich must reveal the names of the others involved in the affair, or else her act will be exposed as a vengeful cover-up."

The party said it has taken action over the past year and a half to ensure clean elections and plans to continue working toward that goal. "We will deal with any attempt to carry out actions of the kind described in the article with the utmost seriousness," it said in a statement.

The polygraph test administered to the Labor Party source found him to be telling the truth when he answered affirmatively to questions about whether he was present when a candidate paid vote contractors by check and whether the candidate in question was present and aware of the payment.

Another former minister was also implicated in the report, with the source saying he saw the candidate give a check to that politician in exchange for support in the primary. That statement too was corroborated in the polygraph test.