A fresh branch-stacking scandal has ignited in Bill Short­en's home state, sparking a heated factional brawl between powerbrokers at Labor's latest state conference.

In extraordinary scenes in Melbourne on Saturday, party heavyweights – including recently retired senator Stephen Conroy and Federal MP Andrew Giles – embarked on an angry war of words over membership rorts that insiders say have spiralled "out of control".

Stephen Conroy with Opposition Leader Bill Shorten in 2015. Credit:Alex Ellinghausen

The stoush came as delegates made a renewed attempt to tighten ALP rules after a recent membership surge identified about 1300 "irregularities" in federal seats such as Scullin, Lalor, and Holt – including unusually high numbers of recruits involving people of Indian backgrounds. In some seats, the conference heard, membership had jumped from 150 to 600 people over two weekends – an apparent bid by stackers to wield more power over policy and preselections.

Mr Giles, who represents the seat of Scullin and is an influential figure in Labor's Left, urged members to vote in favour of a motion that would force people to join a local branch (and not just sign up through the party's central system) if they wanted the right to vote for preselections or local conference delegates.