ACT Greens are fighting among themselves for the right to try to unseat Liberal senator Gary Humphries in next year's election.
A bitter stoush has been sparked by the nomination of high-profile former GetUp! director Simon Sheikh and the apparent endorsement he received from federal Greens leader Christine Milne.
Nominations for the party's ACT Senate preselection closed on Monday with two other Greens members putting up their hands.
One of those candidates, Kate Hamilton, on Wednesday said she would be actively running against Mr Sheikh for top billing on the party's Senate ticket.
Describing Mr Sheikh as a ''celebrity candidate'' who had only recently joined the Greens and moved to Canberra, Ms Hamilton said the strength of the party was in its grassroots origins.
''Parachuting in candidates will alienate members like it has in the major parties,'' she said. ''I am surprised Mr Sheikh chose the Senate seat in Canberra as his next career goal. You know Canberra voters don't necessarily reward fly-in fly-out lobbyists.''
Ms Hamilton returned to Canberra last year after living 22 years in Sydney. Between 2004 and 2008 she was a Greens councillor on the Leichhardt Council.
But ACT Greens convenor Simon Copland is angry she has spoken out against Mr Sheikh, whose nomination has been largely welcomed by the local environmental community.
''Kate Hamilton's actions are against ACT Greens process which prohibits preselection candidates from campaigning against each other in the media,'' he said. ''For this reason, the party will take appropriate action in relation to this.''
Mr Copland did not say what that action might be.
Nor did he comment on the fact that Mr Sheikh spoke to Fairfax about his nomination last week and that Senator Milne publicly said she was delighted at his willingness to join the team.
The ACT convenor said Mr Sheikh had approached the Greens in relation to preselection, not the other way around.
''The ACT Greens are a strongly democratic grassroots party,'' Mr Copland said.
Fairfax sought comment from Senator Milne about Ms Hamilton's nomination but got no response.
Ms Hamilton said she had ''enormous respect for Christine''.
Mr Sheikh responded to Ms Hamilton's statement, saying: ''I've found Canberrans to be warm and welcoming and have enjoyed engaging with the membership of the ACT Greens.
''I have a long-term relationship with Canberra and believe my track record shows that I am effective at getting outcomes.
''If I am preselected I will be putting all of my energy towards getting better outcomes for the people of Canberra, particularly in the face of Tony Abbott's job cuts.''
Ballots will go to ACT Greens members in two weeks' time and stay open for three weeks.
The preselection will be decided early in December.
The third candidate who nominated is local Greens member Stephen Darwin.