The Greens will not enter into a coalition with Labor if the major party's plans for Canberra cannot be amended because the ACT "did not vote for business as usual".
Greens leader Shane Rattenbury wrote to party members on Friday to say the party would use the balance of power to maximum effect and stress that all options remained on the table.
"There was a presumption, from the moment the ABC called the election for Labor, that they were the winners because they have the numbers to form government with the Greens. It was affronting to me, and likely to you as members, that the media and Labor treat us as a wing of the ACT Labor party," Mr Rattenbury wrote.
The email, obtained by The Canberra Times, is the strongest indication yet the Greens are prepared to walk away from negotiations with Labor and sit on the crossbench in the 11th Legislative Assembly.
Members of the Legislative Assembly will on Wednesday vote to appoint the chief minister when the parliament sits for the first time since the election.
Mr Rattenbury said the Greens were using the negotiations to let Labor know the Greens had "big new ideas, the experience to implement them, and a huge amount of determination to change life in Canberra for the better".
"Minority government requires compromise. As many of you know from our member survey and consultation meeting last weekend, the Greens are looking at every option, from sitting on the crossbench with no formal agreement on confidence or supply, through to a governing partnership with Greens as part of cabinet," he wrote.
"The discussion among Greens members in the room last weekend validated all those options, with one constant: the arrangement must prioritise getting the best possible outcomes for the community."
Mr Rattenbury said if the Greens chose to sign a parliamentary or governing agreement next week, it would be because the party was confident working within a government was the better pathway to achieving the change the Greens sought.
"If the ACT Greens choose not to be part of the government, instead representing the community on the crossbench, you will know it's because we are confident this is the better pathway to using our balance of power to pursue bolder action from the government," he said.
The Greens will not support newly minted Liberal leader Leanne Castley to serve as chief minister but the party may back ACT Labor leader Andrew Barr to retain the position without having formalised a deal.
Extensive meetings between representatives from Labor and the Greens have been held this week, after the final makeup of the Assembly was determined.
Labor holds 10 seats in the Legislative Assembly after the election, while the ACT Greens lost two seats and now hold four. With 13 seats needed for a majority, the two parties can govern together.
The split means the Liberals could not form a government with the support of two independents. Ms Castley has effectively ruled out working with the Greens to form government.
Labor would be a seat short of a majority if it cut a deal with independents Thomas Emerson and Fiona Carrick.
More than 200 members of the Greens completed a survey, the result of which was understood to narrowly show members were in favour of its MLAs having some cabinet role.
Janet Rice, the former Greens senator for Victorian, led a meeting of party members on Saturday, October 26, to discuss the outcome of the election and the approach the party would take into negotiations with ACT Labor.
The Greens take a consensus approach to making decisions, which the party's rules note means the Greens "accept that the process of consensus is not necessarily a quick process".
"Consensus is achieved when all members present at a meeting agree with a proposed course of action or, if some members disagree with the proposal, these members decide not to oppose the rest of the members' agreement. Consensus is blocked if at least two members oppose agreement to a proposal," the party's bylaws say.
Mr Rattenbury has repeatedly declared the party had not yet decided whether it would seek to hold cabinet positions under a formal governing arrangement with ACT Labor.
Mr Rattenbury on Wednesday said the Greens were still making up their minds about whether to seek positions in cabinet, but said negotiations were continuing with ACT Labor this week.
"We've got a deadline, of course, next Wednesday when the Assembly first sits. We continue to focus really on the issues that went to the election and finding a workable program for the next four years," he said.
A day after the election, Mr Rattenbury conceded his party's messaging on the need for bolder change had not cut through with voters.
"This is not a vote against us. This is a move for the independents and I think they've done an effective job of tapping into a sentiment that was there. There was clearly a desire for change in some parts of the community," Mr Rattenbury said.
"Whilst the Greens pitched a program of change from within, that's clearly not quite what the community was looking for."
