Green Party MP Eugenie Sage says there are significant environmental benefits to having mana whenua at the table.
"It is those mana whenua kaitiaki responsibilities for air, for the whenua, for soils, for fresh water, for the wai, the awa, for the coastal waters that really need to be at the table of the Canterbury Regional Council because it's got statutory responsibilities under the Resource Management Act for managing all those natural resources," she said.
In 2010, the National Party replaced the regional council with commissioners.
Six years later, Environment Canterbury moved to a 'transitional governance arrangement' - which included two members appointed on the recommendation of Ngāi Tahu.
That was repealed in 2019.
Te Tai Tonga MP Rino Tirikatene is sponsoring the Canterbury Regional Council (Ngāi Tahu Representation Bill). He says it will reinstate that representation.
"Having that mana whenua present at the council table is so important. The other areas which are so important is that having that knowledge and expertise can lead to better decision making," he told Parliament.
The Māori Affairs Select Committee suggested expanding the membership from 14 representatives to 16, so the two new appointees don't come at the expense of others.
National's Paul Goldsmith is worried the two Ngāi Tahu representatives won't be held to the same accountability at the ballot box as the elected officials.
"'Throw the bums out!' is a very fundamental part of democracy, but under this bill, there is no ability to do that. Ngāi Tahu will continue to have two representatives, regardless of how they perform and how the public thinks about them. So that fundamental part of our democracy is abandoned," he said.
Liz Brown co-chairs the Te Rōpū Tuia collective, which represents the 10 Papatipu Rūnanga within the regional council's boundaries.
She says Goldsmith's comments diminish the skill sets the representatives will bring to the role.
"We have over 74,000 registered members, so have a wide pool to select from. We'll be selecting the best people for the role, not the most popular as can happen in a general election process."
The bill has support from the Christchurch, Selwyn and Hurunui District Councils.
Crown Law has advised it does not breach the Bill of Rights.
But ACT's Simon Court insists it's undemocratic.
"This is going to result in unelected members having much greater voting powers compared to democratically-elected members. It's a completely unacceptable act to Cantabrians and to most New Zealanders," he said.
Brown says a lot of the opposition is because people see change as a threat to the way things have always been.
"That does bring fear and it does bring apprehension for people. But I think it's something we have to move through, as a country, and we have to learn to do it in co-governance. There'll be a level of discomfort for some until it becomes the way we just operate."
Tirikatene says it's unlikely the bill could be duplicated in any other region of the country.
"We are dealing with a discrete, very large geographic regional council area, and a single iwi which has vast connections, as we all know, to Te Wai Pounamu, through the South, and is a major player, in their own, in the South Island economy and in society in general."
A previous attempt to reinstate the membership was voted down in 2019, after New Zealand First sided with National.
This time, Labour's majority means it's likely to go all the way.
The government hopes to get it over the line before the local body elections later this year.