The long-running spat has cost the party dearly. Documents seen by The Age show one-third of the Greens' Victorian members quit the party in the 21 months to December, with more resignations expected to follow – even as the party prepares for a looming federal election.

As The Age revealed on Friday, Ms Bhathal walked away from the Greens after 18 years, dismayed at what she describes as a "brutal" and "sanctimonious" internal culture that sabotaged the party's chances of winning the federal seat of Batman from Labor.

Ms Bhathal says she has been subjected to "relentless organisational bullying" within the Victorian branch, claiming the Greens have a "gross problem with governance and process" that threatens to derail the party.

"This is a monumental decision for me; it's probably one of the hardest decisions of my life," she told The Age.

"The Labor Party's culture is highly factionalised and brutal but I feel like the Greens have grown another culture which is just as brutal, but also sanctimonious."

Ms Bhathal's bombshell is a pre-emptive strike. The Victorian branch is due to hold its state council meeting on Saturday, at which Ms Bhathal was to face a censure motion for "allowing herself to be quoted" in the media last year about her grievances with the party.

An internal report to the state council, recommending Ms Bhathal be censured, shows just how sensitive the party is to criticism.

"It should always be recognised that the media is generally not interested in promoting material which supports us but can be assumed to run any story that portrays us in a negative light," it says.

"This is the reason that any, and every, AGV [Australian Greens Victoria] member must not allow themselves to be drawn into providing any comment to the media".

Internal membership figures show just how damaging the past two years have been, with the party bleeding members.

Between March 2017 and December 2018, the party lost 30 per cent of its Victorian membership, from 3962 paid members to 2750.

The decline largely came in a state election year, when on previous trends the membership should have grown.

Ms Bhathal has stood as a candidate for the Greens in Batman in every election since joining in 2001 (except 2007, when she stood as a Senate candidate). She is largely credited with taking the electorate from being an overwhelmingly safe Labor seat in 2001, to one won by the Greens on primary votes in 2016 (the party lost on preferences).

When she was preselected as the Batman byelection candidate in 2017, Ms Bhathal won that vote with a huge margin of 233 votes to 19.

But the Greens' campaign for Batman in last year's byelection was overshadowed by internal warfare.

Ms Bhathal's opponents, she said, lodged failed challenges to her preselection with the Greens' endorsement review and probity panel, and also delayed her preselection in an attempt to find another candidate.

Last January, a 101-page dossier of complaints about Ms Bhathal – signed by 18 members of the Darebin branch, including four councillors, and calling for her to be expelled from the party – was sent to party authorities and leaked to the media, once the campaign for Batman was underway.

The dossier alleged a range of misconduct on Ms Bhathal's behalf, including bullying and intimidation. Among the allegations, Ms Bhathal was said to have stood in front of someone at a press conference, to have unfriended someone on Facebook and to have missed a deadline to have a leaflet printed.

The efforts to undermine Ms Bhathal's candidacy, and a strong campaign from Labor star recruit Ged Kearney, saw Labor hold its seat with a 3.4 per cent swing.

"We were so close to winning, but the constant stream of negative news stories took their toll," Ms Bhathal said.

"I have been loyal to the Greens but I feel like the party showed that they were prepared to tolerate people who would sabotage that – a second winnable lower house seat; a historic achievement."

In January, Ms Bhathal was told the Greens disputes panel had opened an investigation into complaints that were "similar or identical" to complaints previously investigated. A previous investigation into the 101-page dossier found no evidence of wrongdoing on her behalf.

"I have come to the realisation that I can no longer subject myself to this continuing organisational abuse," Ms Bhathal said.

"This has been a recurring nightmare for myself and my family. I am exhausted and worn down. The emotional trauma has at times been too much to bear. It has contributed to the breakdown of my marriage of 23 years."

On Friday, after she dropped her bombshell, Ms Bhathal was bombarded with messages of support from current and former party members. Many told her they, too, intended to quit the party.

A spokesman for the party's federal leader, Victorian senator Richard Di Natale, said the leader would be making no comment on the matter. Party insiders say he has been reluctant to get involved in the stoush.

A social worker, Ms Bhathal has repeatedly rejected any suggestion she behaved aggressively towards campaign staff or volunteers.

"The truth is, I have never bullied anyone; I have never intimidated anyone, I have never harassed anyone."

Instead, Ms Bhathal says the party's grievance processes have been usurped by her detractors in an attempt to wear her down and force her out of the party.

Last year she resigned as the party's candidate for Batman – now renamed Cooper – in this year's election. Now, she will leave the party altogether.

"I feel like things have gotten so nightmarish," she said. "The party has such a gross problem with governance and process. And I have to go."