Radical Balad MK Heba Yazbek said a vote of support for Lapid amounts to one for Naftali Bennett - since the two are in talks for a coalition government.
Yazbek's Balad announced it would not place support behind any candidate and urged all members of the Joint List to follow step.
The MK said, however, that she would respect any decision by the Hadash and Ta'al lists of the party.