The New South Wales Greens MP Jeremy Buckingham has hit back at calls from Richard Di Natale for his resignation, telling his federal leader he should instead voice his support for “the presumption of innocence”.

The NSW Greens have been gripped by damaging in-fighting this week, following a speech by state MP Jenny Leong calling on Buckingham to resign over his alleged inappropriate behaviour towards women.

Leong used parliamentary privilege to accuse Buckingham of an “act of sexual violence” towards Greens aide Ella Buckland in 2011. She also levelled unspecified allegations against Buckingham over behaviour she said had driven other female volunteers and members from the party. Leong also alleged he had acted aggressively towards her twice this year.

Buckingham denied the allegations and pointed to an independent investigation that found there was insufficient evidence to substantiate the Buckland complaint.

Following Leong’s speech, Di Natale called for Buckingham to resign. He was joined in that call by the federal Greens senator for NSW, Mehreen Faruqi, and others in the party.

But on Thursday Buckingham wrote to Di Natale calling on him to make a public statement in support of “the presumption of innocence and procedural fairness”.

The letter, obtained by Guardian Australia, said: “If we abandon the vitally important principles of a presumption of innocence and procedural fairness in an attempt to placate the Left Renewal faction that has infiltrated our party, then what kind of party is the Australian Greens,” he wrote.

“I request that you make a public statement re-affirming your support for the principles of the presumption of innocence and procedural fairness.”

The Left Renewal referred to by Buckingham is a radical, hard-left faction within the Greens, characterised by its blanket opposition to capitalism and opposition to state power. It is centred around former senator Lee Rhiannon, among others, though Rhiannon said she was not a member.

Faruqi, one of those calling for Buckingham’s resignation, openly clashed with Rhiannon and her left faction during a fierce preselection battle last year.

Other state MPs, including Cate Faehrmann and Justin Field, have come out in support of Buckingham and criticised Leong’s speech.

Field said it was an “orchestrated political hit” designed to push Buckingham from office.

In her speech to parliament, Leong said the push to remove Buckingham was not motivated by internal party politics.

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