The Labour Party says the government has not done enough to protect land from foreign ownership after agreeing to the Trans-Pacific Partnership deal.
Labour's Māori development spokesperson, Nanaia Mahuta, said the government has put Māori land interests second in line to multilateral trade interests.
She said that included not lifting the threshold for sale of land to foreign owners.
"The agreement hasn't been open to public scrutiny and while the government has put out a Q&A explanatory note I think there are a number of concerns that Māori have that will need to be better scrutinised.
"In particular, obligations under the Treaty, but more specifically in terms of the sale of foreign land, lifting the threshold so that land isn't opened up carte blanche for foreign ownership, because we've already had problems in that area."
Ms Mahuta said she was concerned that the Māori voice had not been heard.
"Waitangi Tribunal action has been taken because Māori are concerned about the impact of the TPP on intellectual property rights and traditional knowledge and all manner of things. There's been very little participation by Māori in this process."
The MP said she did not believe there was widespread support for the Federation of Māori Authorities' backing of the TTP agreement.
As the industry body for the Māori economic sector, the federation (FOMA) represents over 150 Māori authorities.
"I haven't heard any promotion of that view amongst wider iwi Māori forums so I'm a bit dubious with regards to the mandate that FOMA carries to be able to endorse the TPP in the way that it has."
She said while the TPP agreement would be sent to the Foreign Affairs Select Committee to be examined, Māori should also have that opportunity.
"The Treaty provisions should go to the Māori Affairs Select Committee so that it can be scrutinised properly and so that there is an opportunity to go through the various concerns that Māori have and test the robustness of that Treaty clause."
Trade Minister Tim Groser responded to a request for comment with the following statement:
"Ms Mahuta and the Labour Party should be supporting TPP as it will be enormously beneficial to Māori exporters who are predominantly involved in the primary sector.
"The government has successfully included a specific provision preserving the pre-eminence of the Treaty of Waitangi in New Zealand.
"Nothing in TPP will affect the status of Māori owned land or prevent the Crown from meeting its obligations to Māori."