Green Party co-leader James Shaw says Act Party leader David Seymour should apologise over comments comparing new Māori ward legislation to apartheid in South Africa.
Rotorua mayor Steve Chadwick has also weighed in on the issue, saying Seymour should "become relevant".
Shaw was in Rotorua on Friday visiting Crown research institute Scion, Te Arawa fisheries and Rotorua Lakes Council, where he discussed the council's recently approved Climate Change Action Plan.
On Wednesday, Seymour said the Local Electoral (Māori Wards and Māori Constituencies) Amendment Bill, which passed its third and final reading on Wednesday evening, was "better described as the Apartheid Bill".
He said the bill would not solve the fundamental economic and social issues the nation faced, and was underpinned by a "basic assumption … that our country has two categories of people with different legal rights".
The law means the public can no longer veto a council's decision to introduce Māori wards.
Shaw called Seymour's comparison of the Māori wards bill to apartheid "offensive and ignorant".
"The idea is ... no comparison and utterly offensive.
"Apartheid was a system developed by a white minority to keep control over a black population in South Africa."
He said Te Tiriti o Waitangi should have already "flowed through ... into our governance arrangements".
Shaw said Seymour should "withdraw and apologise" and "get with the programme".
He said all councils should have Māori wards.
"It's just a logical extension of our Te Tiriti obligations. It's just how that flows through in practical matters into how we govern the country. We do it at central government, what is the distinction?"
Rotorua mayor Steve Chadwick, a former Labour minister, said Seymour should "become relevant".
On Friday, in response, Seymour said the principle of Māori wards was that people's membership of an ethnic group was more important than their character.
"If James Shaw, or Steve Chadwick, or whoever else, want to explain why that principle is different to apartheid, they're very welcome.
"On the other hand, if they accept the principle's the same and want to argue Māori wards differ only in the extent I think that's a perfectly valid position.
"The same applies to their interpretation of the Treaty. Act says it gives the same rights and duties to every person, but they want to make it a partnership between two collectives where your membership of an ethnicity is more important than your dignity as a person."
In August 2020, Tauranga City Council voted to introduce Māori wards, but that plan was scuppered when a petition calling for the decision to go to a referendum met the threshold to force it.
That threshold was 5 per cent of electors, and if the local referendum found electors to be opposed to the change, it would be vetoed. The new law saw an end to this veto power.
In 2015 Rotorua Lakes Council and Te Arawa set up a partnership arrangement through a manawhenua representative group, Te Tatau o Te Arawa, which had voting members on council committees, but not at council level.