The New South Wales Greens MP Jeremy Buckingham is considering legal action after he was formally asked not to recontest his upper house seat at the state election in March.

In a statement on Sunday, Buckingham said the party processes had been “abused and co-opted for factional purposes” and that grassroots members had been “disenfranchised” by a move to eject him from the party.

“The party’s own constitution specifies that the election ticket for the Legislative Council is set by a democratic ballot of all Greens members,” Buckingham said.

“It is in black and white and it was written that way precisely to stop MPs and party insiders from meddling with preselection results.”

He added: “I will be assessing my legal options and I will have more to say in a few days’ time.”

The push against Buckingham follows allegations made in parliament by fellow NSW Green Jenny Leong accusing Buckingham of sexual misconduct against a staffer, Ella Buckland, in 2011.

An independent investigation was unable to substantiate Buckland’s claims and Buckingham strenuously denies them.

On Saturday, the party’s state delegate council passed a motion calling on Buckingham to remove himself from the Greens upper house ticket, saying the council believed that “if Jeremy Buckingham remains on the ticket for the 2019 NSW election, the Greens NSW will not be able to campaign effectively on the issues which we all know are so urgent”.

The motion also thanked him “for his extensive and outstanding campaign work against coal and coal seam gas, and for a sustainable Murray-Darling Basin in NSW”.

It was the third attempt to unseat Buckingham made at the council, after two earlier motions, including one that said the party had lost confidence in Buckingham, failed to get the required 75% of votes.

The Greens’ federal leader, Richard Di Natale, and federal MP Mehreen Faruqi have also called for him to stand aside.

Buckingham said the party had “abandoned grassroots democracy by overturning a democratic preselection result” and that the party’s organisation was “corrupt and rotten”.

“I’d like to thank the many people who have offered me support over the past few weeks,” he said. “I know many members and supporters are shocked at what has been happening.”

NSW upper house Greens MP Cate Faehrmann made a statement in support of Buckingham saying she was “beyond appalled that the party I have been a part of for almost two decades and have poured my heart and soul into has voted to attempt to force a popular and hugely effective MP to resign.”

Faehrmann had previously accused Leong of using allegations of sexual misconduct “as a political weapon” and said the push against Buckingham was not about women.

In a statement on Facebook, Faehrmann said reports that she and fellow MP Justin Field had urged Buckingham to resign were “simply not true” and that those reports were used in the state council meeting, which she did not attend, to “wear people down, one by one, and bully them into submission.”

“It is my firm belief that the party in NSW has been infiltrated by destructive extreme left forces who will stop at nothing to weaken those in the party, like myself and Jeremy, who want nothing more than to make a difference for the planet, our climate and our future,” she said.

Leong made a statement under parliamentary privilege in November accusing Buckingham of committing an “act of sexual violence” against party aide Ella Buckland in 2011.

“Jeremy, you have had countless opportunities to take responsibility for this, to apologise to those impacted, and to seek to address them. Instead you have followed with further aggressive tactics,” she said.

“I know you feel like you are the victim of internal party attacks, but you must acknowledge your role in this and stand aside before more damage can be done.”