The split in the NSW Greens has intensified with the establishment of a breakaway secret Facebook group that has banned members deemed to be "nasty".

The NSW Greens Supporters (No Nastiness) group was set up in early September by Jack Gough, a staff member of Greens MLC Jeremy Buckingham.

It follows ongoing hostility between Greens members on an existing group, including after the bitter contest to select a successor in the upper house to Greens MLC John Kaye, who died of cancer in May.

The contest came down to one between Justin Field – supported by Mr Buckingham – and candidates aligned with Dr Kaye and Senator Lee Rhiannon - sometimes referred to as the "eastern bloc".