The selection of a replacement for the late Greens MP John Kaye in the NSW upper house is descending into a nasty internal fight, exposing the deep ideological split in the party's state division.

From Monday about 4000 NSW Greens members will vote on a replacement for Dr Kaye, who died of cancer in May. There are 14 candidates contesting the ballot, to be determined in August.

Greens members are at war over who will replace John Kaye in the NSW Legislative Council. Credit:James Alcock

A group ideologically-aligned with Dr Kaye and his ally, Senator Lee Rhiannon – sometimes referred to as the hard left faction, or "eastern bloc" – is being accused of running a "damaging" ticket in a bid to have preferences directed to its eight candidates in the optional preferential voting system.

Included in the group are leading preselection contenders James Ryan, Bruce Knobloch and former Kaye aide Kelly Marks.