Ngati Whatua says it will refuse to take part in any powhiri for international trade ministers when they visit New Zealand to sign the Trans-Pacific Partnership on February 4 because it opposes the agreement.
Piripi Davis, chairman of the tribe's Orakei trust board, said its "strong opposition" to the TPP meant it would not participate in welcoming ceremonies when ministers from the 12 TPP countries gather in Auckland for the signing.
A spokeswoman said the iwi had not yet been asked if it would take part in the powhiri, but in the past it had done so for visiting dignitaries as it had mana whenua status in central Auckland.
It was letting the Government know ahead of time that it would not take part.
Mr Davis said the iwi had supported New Zealand's bid to win a seat on the United Nations Security Council.
"We hosted dozens of UN ambassadors on our marae and welcomed them in a joyous occasion where they could experience our culture.
"We supported that Government initiative because it was building relationships between peoples and nations.
"We cannot support or agree with this particular issue because, in our view, the TPPA will harm not only our people but also New Zealand and its people overall."
Mr Davis said there had been a lot of anger and mistrust voiced about the TPP, and he agreed. The iwi's stance was also out of concern about the commercialisation of traditional uses of indigenous flora and fauna.
The Ministry of Foreign Affairs and Trade could not immediately say whether it already has a group arranged for the powhiri.
Ngati Whatua's stance follows calls from Ngapuhi elder Kingi Taurua for his tribe to refuse to welcome the Government onto Te Tii Marae at Waitangi on February 5 if the National-led Administration goes ahead with the signing.
Ngapuhi is due to hold a hui on February 2 to make a final decision.
Prime Minister John Key has said he intends to travel to Waitangi, but will not "gatecrash" the lower marae if he is not welcome.