Yitzhak Herzog, Shelly Yechimovich
Yitzhak Herzog, Shelly YechimovichTomer Neuberg/Flash 90

As Opposition head MK Yitzhak Herzog faces a criminal investigation on suspicions he breached funding laws, Zionist Union is preparing for the possibility that the investigation will prevent Herzog from leading the party.

There are many contenders in the Labor faction who apparently have already started vying to be chairperson of Zionist Union, a joint party with MK Tzipi Livni's Hatnua.

Their numbers include former Labor head Shelly Yechimovich, Erel Margalit, Eitan Cabel, Amir Peretz, and possibly even Tel Aviv Mayor Ron Huldai.

According to internal party polls, Yechimovich soundly defeats her opponents by obtaining over 40% of the support of Labor voters, reports Channel 10 on Tuesday.

Despite those results, according to the report the party is seeking to avoid Yechimovich's return to power - if Herzog is forced to step down MK Eitan Cabel will be placed as the temporary chairperson until Herzog's fate is determined.

If Herzog is unable to return to serve as party chairperson then Labor will hold primaries, and according to Zionist Union members such a turn of events would evidently give Cabel an edge over Yechimovich.

Herzog is suspected of breaching funding laws through an external NGO during the 2013 Labor party primaries, when he defeated Yechimovich and took over leadership of the Labor party from her.

At a Labor party event on Tuesday, Herzog said he was "perfectly calm" despite the investigation.

Less than an hour before Herzog's comments, Yechimovich hinted that Herzog should consider stepping down over the controversy - echoing similar views aired by another fellow MK earlier in the day.