The Council of Trade Unions (CTU) is calling on the Waitangi Tribunal to agree to hold an urgent hearing into the Trans-Pacific Partnership.
The tribunal on Thursday heard opposing arguments from the Crown and Māori on whether it should hold an urgent inquiry into the proposed trade deal.
CTU Vice-President (Māori) Syd Keepa questioned the Crown's commitment to the treaty when it would not engage in discussions about the TPP.
"I would have thought that iwi Māori would have been involved in it from the word 'go' but it just seems to me that the negotiations itself is full of secrets.
"We don't know what is going to happen nor do Māori know what is going to happen, so I am very concerned about what will happen to our tino rangatiratanga in the future."
He said he has serious concerns for Māori workers if the TPP agreement is signed.
"There has been stuff that has come out in other countries where a couple of corporates have sued. One was because the country increased the minimum wage so that rings [warning] bells for me as someone who supports workers."
Mr Keepa said the tribunal should listen to concerns around the TPP and take it seriously.
"We want them to sit down and listen to the concerns of the people at the coal-face and to iwi Māori".
The Crown has defended the secrecy around the negotiations.
Solicitor General Mike Heron said yesterday that the Crown had engaged in meaningful talks with Māori during the TPP process.
He said it had consulted widely, including with Te Puni Kōkiri and Māori industry groups.
If an agreement on the TPP is reached, it is scheduled to be made public in August 2016.