The Green Party says it will support the Government if it wants to introduce a capital gains tax and may also support a land tax.
The Government is considering signficant changes to the tax system, following a report this week by a tax working group which suggested a range of measures to make the system more fair and efficient.
Green co-leader Meteria Turei has pledged the party's nine votes to support one of the more contentious recommendations of the working group, a capital gains tax.
Green Party co-leader Russel Norman says almost every other developed country taxes the money people make through trading property.
He says it's unfair to tax income from wages but not income gained by selling property.
Dr Norman says the country needs a tax system that helps to close the gap between the rich and the poor.
Ms Turei says the party would also give consideration to a land tax, but that support is conditional.
She has ruled out supporting any tax package which included an increase to GST or cuts to top income tax rates.
Ms Turei says reducing the tax paid by those on high incomes, while increasing the cost of all goods by lifting GST to 15%, would simply make life harder for those who are already struggling.