Meretz leader Nitzan Horowitz called on Friday for Labor and Meretz to run together in the next election, but Labor leader Merav Michaeli said the parties should run separately and take back votes from Yesh Atid and Blue and White.
Speaking at the Berl Katznelson Fund's annual conference, Horowitz said he would want to see a united social democratic party.
"Meretz and Labor need to go together," he said.
Labor and Meretz ran together in the March 2020 election, together with the Gesher Party of current Likud MK Orly Levy-Abecassis.
In her speech at the event, Michaeli spoke about the need for Labor to return to its former role as the dominant party in the Center-Left bloc. She said the rise of opposition leader Benjamin Netanyahu caused "post-trauma" that divided the bloc and led to the formation of what she called "undemocratic parties" - a reference to Yesh Atid and Blue and White.
"Our bloc must do everything possible to rebuild the democratic parties, which are of course Labor and our sister party, Meretz, to restore our party and stop dividing and dispersing out camp's votes," Michaeli said.
There were reports that Michaeli did call for Labor and Meretz to run together, which put the party on the defensive.
Labor faction chairman MK Ram Shefa, who entered in politics in Blue and White, told KAN on Saturday that Labor would continue to represent both centrists and left-wingers.
"There will not be a union with Meretz," Shefa said.
Labor secretary-general Eran Hermoni said "Labor is not a branch of Meretz" and "must return to its rightful place in the Center-Left."
Michaeli said it was not the time to talk now about elections, because "that creates a dynamic of elections." She said she would do everything she could to keep the current government in power.
Aaron Reich contributed to this report