The Emissions Trading legislation is a step closer to being debated with the Green Party now pledging its support.
But the Government is still waiting for New Zealand First to make a decision, before it will bring the bill back to the House.
The Government now has 56 votes for the bill, including support from Progressive Party leader Jim Anderton and the Greens.
If New Zealand First joins them, that will push the numbers up to 63, a slim majority of five votes.
Party leader Winston Peters says the issue was discussed at caucus on Tuesday but as two of its MPs were absent, no conclusion was reached.
Mr Peters will not say when a decision will be made. If it is on Wednesday, the Emissions Trading bill is likely to be debated when the House resumes on Thursday.
Greens secure 'significant' changes
Greens co-leader Jeanette Fitzsimons says her party has secured significant amendments to the scheme, including a $1 billion fund, to be spent over 15 years, to help insulate homes.
The insulation work will be funded from money generated by the emissions trading scheme.
But Ms Fitzsimons says the scheme in itself will not do enough to reduce carbon emissions.
Other changes to the scheme include plans for a government target for emissions reductions and a cash payment to households to help offset higher power prices when the electricity industry comes into the scheme in 2010.
Onus on business, says lawyer
An energy and resource lawyer says the Green Party's decision to back the Emissions Trading Bill puts the onus on business to prepare itself.
Bryan Gundersen, a senior partner at Kensington Swan, says the implications for businesses will be immense.
He says the two-month break while the Government has been garnering support for the bill has lulled some companies into a false sense of security.
Mr Gundersen says overall operating costs for many businesses and households will increase as a result of emissions trading, but there will also be new business opportunities.