Opposition agriculture spokesman Gavan O'Connor last night lost preselection for his seat of Corio, near the Victorian city of Geelong, west of Melbourne.
Mr O'Connor was defeated by union leader, Richard Marles.
Labor's health spokeswoman, Julia Gillard, has called for an end to factionalism within the party.
"It's time to stop mincing words and to acknowledge that factionalism in the Labor party is out of control and destructive.
"We need to break the nexus between branch stacking and being rewarded with jobs."
The former Labor leader, Simon Crean, fought off an attempt to remove him from his safe Victorian seat earlier this week.