Iwi say they have paid enough tax on Treaty settlement money and must get exemptions if a capital gains tax is introduced.
Iwi Chairs Forum spokesman Ngahiwi Tomoana said many iwi felt like they had been taxed enough.
"Our treaty settlements, they were only settled at two percent of their real value, and we already think we have been taxed 98 percent of our treaty settlement.
"One of the issues we were considering was how do we mitigate this huge tax burden of 98 percent on treaty settlement, whereas the Tax Working Group only wanted to consider current-day capital gains tax."
In February the Tax Working Group recommended a capital gains tax be introduced.
Mr Tomoana said if the tax was brought in, some iwi transactions must be exempt, such as selling assets to buy ancestral land and moving assets from iwi to hapū to marae.
"If it was recovering traditional lands or traditional assets, we say that capital gains should not apply. But if it was the acquisition of other properties or other assets, then it could apply."
The Tax Working Group recommended a a capital gains tax was not applied to iwi if they were shifting assets within the tribe, because they were essentially the same owner.
Parininihi ki Waitōtara chair Hinerangi Raumati, who was on the group, said they also proposed exemptions on selling assets to buy ancestral land.
"They do not get back ancestral land - they do not get back land that matters to them, they just get back what they get.
"At a later point in time, they might want to buy back a special piece of land if it comes up for sale. So, we have said, if they have to release assets to do that, then there should not be an impact in terms of the capital gains tax."
It also proposed an exemption or rollover relief for Māori land under Te Ture Whenua Māori Act, because it came under a complex layer of rules that did not apply to other land.
Ms Raumati said, for the most part, iwi would be treated in the same way as everyone else, and they accepted that. But she said they had a point about their Treaty money.
"Iwi have a case just on the basis that the settlements that came back to them are about two percent of what was lost," Ms Raumati said.
"For me there is always going to be a case for saying that imposing more tax or imposing more rules...simply adds to the burden."
Māori Council executive director Matthew Tukaki said there was a lot of uncertainty about how the capital gains tax might work and what would be exempt. He was encouraging iwi to think ahead.
"One of the things I have been telling iwi and hapū over the last few weeks is if you are in the midst of negotiations, you need to be considering whether or not you introduce clauses around the impact of a future capital gains tax."