Former premier Nathan Rees sounded the warning as senior Labor figures described as "baffling" and "inexplicable" the determination of Sussex Street to protect Ms Hay, a longtime ally of Eddie Obeid and Joe Tripodi during their time in Parliament.

Fairfax Media has spoken to an ALP member who claims to have come under pressure from a head office operative and was warned to rethink supporting Ms Hay's opponent in the upcoming preselection ballot, University of Wollongong academic Paul Scully.

Warnings have also been made against careers and political aspirations based on support for Mr Scully. "There have been a lot of threats, lots of head office dirty tricks," said an individual who did not wish to be named.

Labor's disputes committee will rule on the eligibility of some branch members to take part in the vote before it takes place on December 6.

Concern at the tactics of Sussex Street has made it as far as Canberra, with a number of federal Labor MPs concerned that the matter marks a backward step in the process of cleaning out connections to the Obeid-era and curbing their interventions of Sussex Street

A senior Labor source said it was known in the Right that head office wanted to hold on to someone in caucus who could be relied upon to "report back to them". Ms Hay has been the convener of the Right faction in caucus ever since she was backed into the role by Mr Obeid and Mr Tripodi and is said to be "joined at the hip" with the party machine.

As a member of the Left when she entered Parliament, Ms Hay supported Ian Macdonald into the ministry before defecting to the Right. All three former colleagues have had corruption findings made against them by the Independent Commission Against Corruption and Mr Obeid and Mr Macdonald are now facing criminal charges.

Mr Rees said: "Noreen Hay has had a long career in the Labor Party and it is a matter for the leader [John Robertson] and head office whether she retains their backing. But any rebuilding of the Tripodi-style model of caucus should be resisted by branch members at all costs."

Another former premier, Morris Iemma, said all sitting members should have the right to recontest their seats but head office should not interfere in the outcome of a vote.

"It should be a fair and open vote. I know from the reputation Noreen has [for maintaining support in local branches] that she will win it," Mr Iemma said.

But Labor insiders point out that head office appears comfortable to allow the career of Auburn MP to end amid allegations of branch stacking by her opponents but is actively working in favour of Ms Hay.

"Noreen was a big part of the old show. It's a missed opportunity," said a source.

Mr Scully formerly held the position of returning officer for the NSW ALP and has the support of Nick Whitlam, son of the recently deceased Labor giant, Gough.

He is expected to receive strong support in a vote but Ms Hay will have the advantage of a 20 per cent loading as a female candidate. Wollongong councillor Ann Martin, a member of the Left, will also contest.

General-secretary Jamie Clements declined to comment.