Labour is still waiting for New Zealand First to confirm its support for its flagship emissions trading scheme, but yesterday it won the crucial votes of the Greens.
Winston Peters' party is expected to follow suit shortly.
The Greens agonised over whether to back the major climate change policy at yesterday's caucus meeting and after a frank exchange of views the party's six MPs agreed to say "yes" to Labour.
The outcome was expected, although the Greens feel it is unfair that the agriculture sector isn't going to be included in the scheme for several years.
The party remains concerned the scheme simply doesn't do enough to reduce emissions.
While anxious to outline what they got in exchange for their support, the Greens made it clear they will campaign on further improving the response to climate change as they head into the election.
"On balance, and given the very significant changes that we have achieved, we have decided that it is better to make a start than to do nothing," Greens co-leader Jeanette Fitzsimons said.
"There were strong views expressed in the caucus and all of us had quite mixed feelings - but in the end we reached a consensus."
New Zealand First also discussed the emissions trading scheme in a caucus meeting yesterday but did not come to a final decision, apparently because two of its MPs couldn't get to the meeting.
One had the flu and another was stuck in Dunedin.
"Shortly yes, but not yet," leader Winston Peters said when asked if a decision was near. New Zealand First may also want to delay its decision to gain maximum exposure from the wins it has got in negotiations.
Sewing up the support of the Greens means Labour needs only New Zealand First's seven votes to get the emissions trading scheme passed into law.
Prime Minister Helen Clark has been desperate to get the legislation passed before the election after pushing the issue to the front of her political agenda.
All the signals are that New Zealand First will back the scheme, having secured some compensation for people who will be affected by higher electricity bills.
Ms Fitzsimons did not want to go into the detail of that compensation yesterday but indicated it was universal - meaning everybody will get something when electricity enters the scheme in 2010 - and its level would be based on household income.
It would take the form of a cash payment.
Helen Clark said she was "very appreciative" of the Greens' support and expected to hear from Mr Peters soon.
The Prime Minister added that the compensation package was a "very good" one and it looked after "vulnerable consumers".
National intends to change the emissions trading scheme if it wins the election.
Ms Fitzsimons said post-election negotiations were an opportunity to negotiate on anything, in a clear hint her party will also try to change parts the scheme if it has bargaining power following the election.
WHAT GREENS GOT FOR SUPPORT
* $1 billion over about 15 years to insulate and upgrade low-income homes to make them warm and dry. Higher-income homes will also get a substantial subsidy.
* A commitment from the Government to develop and implement a National Policy Statement on biodiversity no later than February 1, 2011.
* A contestable fund of 150,000 carbon credits a year for people developing new technologies that will reduce carbon.
* Plans on how to allocate permits - which will be decided by regulation - will be scrutinised by Parliament.
* The legislation will require the minister to gazette targets for carbon reduction.
* A small target for emissions reduction from agriculture before 2013 will be gazetted, and research funds in the sector will be spread into sustainable solutions and not just chemical ones like nitrification inhibitors.