The New South Wales Greens are in the grip of factional infighting as Senator Lee Rhiannon backs a complaint designed to oust the state upper house member Jeremy Buckingham from the party over criticism of her on the ABC’s Four Corners.

Buckingham has emailed all federal Greens parliamentarians labelling the move a “factional attack to try to usurp a grassroots preselection”. His fate will be decided by a complaints committee of four randomly selected Greens office holders.

In the Four Corners episode, aired in August, Buckingham accused Rhiannon of thwarting democratic reforms such as the direct election of office bearers and broadcast of the state delegates council.

In November Rhiannon lost a preselection battle for the top of the federal Senate ticket in NSW to the state upper house member Mehreen Faruqi after a chorus of Greens including the federal leader, Richard Di Natale, Senator Nick McKim and the former leaders Christine Milne and Bob Brown bucketed her in the program.

The complaint, seen by Guardian Australia, accuses Buckingham of “serious and false criticisms” and is signed by eight members, including two who Buckingham described as members of the socialist Left Renewal faction.

It includes supporting statements from Rhiannon and her partner, Geoff Ash, in which they deny Buckingham’s charge that they demanded he denounce Brown as a “megalomaniac”.

The complaint says it is untrue that Rhiannon blocks democratic reform and argues the claims bring the party into disrepute: “Jeremy’s comments about democratic reform are a litany of inaccuracies and slurs about the party and our senator. They are unprovoked and untruthful public attacks on our party and a Greens colleague.”

The complaint argues that even if Buckingham’s claims were true it was “grossly disloyal” to air them in public rather than complain through internal processes.

The complaint submitted that Buckingham should be expelled from the NSW Greens or at the least “suspended for many years”. The signatories reject the prospect of mediation, arguing it would be a waste of time because Buckingham has shown no sign of contrition.

It notes Buckingham’s service in the mining portfolio campaigning against coal seam gas but warns that “no Greens member and no Greens MPs are indispensable to the success of the party”.

“No person’s membership of the Greens is sacred, particularly when their behaviour causes many others to leave the party, or decide not to join.”

Buckingham alerted the federal Greens to the complaint in an email on Monday in which he said none of the complainants had raised the issues with him at any point.

“Unfortunately the NSW Greens convenor has decided to escalate the complaint to a conflict resolution committee without asking for, or ordering mediation,” he said. “The conflict resolution committee consists of four members of the NSW Greens who have the power to either reprimand, suspend or expel a member without review.”

Buckingham said the complaint sought to exclude him from preselection to be conducted in April and May 2018 for the 2019 state election.

“There has been considerable procedural unfairness in the handling of this complaint,” he said, citing the fact he had responded to one version of the complaint “in good faith”, only for a longer version with significant new information to be produced.

He warned he would “vigorously defend” any attempts to expel or suspend his membership within the party and in court. “This type of factional attack to to try to usurp a grassroots preselection ballot should have no place in the Greens.”

Rhiannon told Guardian Australia: “I deny the slurs Jeremy Buckingham has made against me. It is inappropriate for MPs to make public comment on internal complaints.”