Wednesday's dramatic move by former emergency services minister Jane Garrett to abandon her key inner-north seat of Brunswick is part of a broader power play by Labor MPs, including Ms Garrett and Adem Somyurek, another former minster still fuming about his sacking from the front bench and determined to return.

Ms Garrett, who is from the party's left faction, and Mr Somyurek, who comes from the right, lead a loose grouping of about 10 MPs who sources allege are now a positioning themselves to put serious pressure on Premier Daniel Andrews, particularly if Labor loses November's crunch by-election in the key inner-north seat of Northcote.

The cross-factional group were described on Thursday as a "coalition of the discontented" who have little in common politically other than a shared dislike of the current party leadership.

"They're kind of united by a disparate anger," one Labor figure said on Thursday.

But one member of the group dismissed that characterisation as "horse shit", on Thursday, rejecting the "discontented" label and saying they were seeking much-needed generational change in the party's factional system, not destabilisation.

Ms Garrett told Fairfax "these anonymous claims are ridiculous and false".

If Northcote falls to the Greens, party figures worry, Mr Andrews will be left clinging to a one-seat majority on the floor of State Parliament and facing a tough election within 12 months, leaving his government vulnerable to disruption from within.

One senior party figure described Ms Garrett's move as "extraordinary".

"The disruptive consequences of this should not be underestimated," the source said.

Party operatives are also complaining bitterly about Ms Garrett leaving Brunswick just as Labor was mounting its campaign for neighbouring Northcote against an expected strong challenge from the Greens.

Some in Labor fear Ms Garrett's abandonment of Brunswick, which will be defended by Australian Council of Trade Unions President Ged Kearney, will be a hammer blow to the morale of party workers and volunteers battling to hold Northcote.

"This plays into the narrative that the Greens run all the time, that Labor is walking away from the inner-city," one insider told Fairfax Media.

Ms Garrett rejected the criticism.

"There can be no greater endorsement of Labor in the inner city than the outstanding national leader Ged Kearney standing for Brunswick," she said.

"My reasons for seeking to move from this seat are well known and I hope would be looked on with compassion."

While Ms Garrett's play for the plum upper house seat in the Western Metropolitan district sparks a pre-selection battle within Labor's left, candidates loyal to Mr Somyurek are battling fellow right faction members for nominations in the safe seats of Tarneit and Footscray, where the sitting members are retiring.

The South-East Metropolitan upper house member is openly challenging the decades-long domination of the right faction by a group loyal to former federal minister Stephen Conroy, which has signalled its determination to fight for its seats.

Mr Somyurek also declined to comment on Thursday.

In Western Metro Australian, Ms Garrett will contest the preselection against another candidate from the left, Australian Services Union secretary Ingrid Stitt.

In Ms Garrett's corner is the powerful CFMEU construction union and a potentially disruptive tussle for the pre-selection votes of about 1900 party members in the area is expected.

"It is all very uncertain, let along hugely risky and destabilising," a party source said.