AT LEAST two NSW Greens MPs are being urged to run for the Senate at the next federal election, setting up a potential preselection battle that would expose the increasingly factional nature of the minor party.

Upper house MP John Kaye confirmed to The Sun-Herald he would consider a switch to Canberra but said he was ''not actively contemplating anything'' at this time. He narrowly missed out on becoming a senator in 2004 before entering state Parliament in 2007.

Sources said he was supported by Lee Rhiannon, the former NSW Greens MP who entered the Senate in July. Ms Rhiannon is from the ultra-left of the Greens and has been labelled a ''watermelon'' by her enemies, green on the outside but red in the middle.

If Dr Kaye, who supports an anti-Israel boycott along with Ms Rhiannon, entered the Senate it would be seen as a significant boost to her power base and possible future leadership ambitions.

For that reason, the Greens leader, Senator Bob Brown, is believed to have approached Dr Kaye's NSW colleague Jeremy Buckingham to run, sources told The Sun-Herald. Along with the veteran Tasmanian environmentalist, Mr Buckingham is seen as a ''capital G'' Green.

Tasmanian-born Mr Buckingham is the party's upper house spokesman on the key issue of mining. His energetic pursuit of the coal seam gas issue is believed to have brought him to the attention of Senator Brown as a future federal MP.

Mr Buckingham said he had not spoken to anyone about a switch. ''I'm very happy where I am, I've only been an MP for six months. No one has come to me about this,'' he said.

Dr Kaye said: ''I'm not actively considering anything. I love state politics and there's a lot of issues I'm working on. It's a lot to give up for a 50:50 chance to win a Senate seat.''

David Shoebridge, who has also been mentioned as an outside chance of being on the ticket, said he was not interested at this point.

Preselection will be completed early next year, with each party member having one vote in the process. Greens MPs are not supposed to openly campaign for their preferred candidate.