Labor MK Amir Peretz handed his resignation letter to Knesset Speaker Reuven Rivlin on Thursday afternoon, hours after announcing he would join the Tzipi Livni Party in upcoming elections.
Peretz will be replaced by former Labor MK Yoram Marciano, who was next on the party's list for the 18th Knesset, but did not run in last month's primary.
"We need to ask ourselves what is happening in our political culture," Rivlin told Peretz. "I come from a very ideological home, and I see a new culture that has brought many Israelis to raise an eyebrow."
Rivlin called for a new code of political behavior to stop the wave of party-jumping.