Former treasurer Wayne Swan is firming as a favourite to win the Labor party presidency as Bill Shorten's supporters line up behind him.
Incumbent president Mark Butler is fighting on a reform agenda, but his spot is under threat thanks to the CFMMEU's decision to run a candidate and split the Left vote.
Labor sources from the Left and Right told AAP Mr Swan was now the favourite ahead of Friday's voting deadline.
The party's rank-and-file leans to the left, but the voting system means whoever gets the most votes wins, leaving Mr Butler vulnerable to losing votes to two other left-wing candidates.
One Labor MP said Mr Swan was the favourite, and being an older, experienced candidate might help him with the party's older base.
The CFMMEU is running maritime organiser Mich-Elle Myers, which will likely split some of the Left vote, while the Left faction's Senator Claire Moore is also running.
The powerful left-wing CFMMEU is locked in behind Mr Shorten as leader, and recently used its muscle at a Victorian conference to shut down debate on changing Labor's stance on refugees.
Mr Swan has voted against party reform measures at previous national conferences, and is instead running on an agenda attacking economic inequality.
The former treasurer has been described as an Aussie version of Bernie Sanders for his push to hit banks and multinational tax avoidance.
"A decade after the GFC, we can now see clearly that rising inequality isn't just making our society less fair, it is making our economy less prosperous, less stable, more fragile and more crisis-prone," Mr Swan said in March.
He's also determined to make sure Mr Shorten becomes prime minister.
Mr Butler won the presidency in 2015 but has largely not been able to achieve the reforms he called for.
Mr Swan is retiring at the next federal election, while Mr Butler is looking for a new seat after his was slated for abolition in a recent boundary redraw.
Labor's national conference has been pushed back due to the Super Saturday by-elections falling on its original July 28 date, so Mr Butler will stay in power until December.
Voting closes on Friday, with the ballot counted and the winner announced shortly afterwards.
