An affidavit from one of the claimants challenging New Zealand's involvement in the Trans Pacific Partnership Agreement argues they've had to seek an urgent hearing because of the Crown's refusal to release information about the progress of negotiations.

The Waitangi Tribunal is holding a meeting on Thursday to hear further submissions on why their claim should be heard urgently.

Photo: RNZ / Anusha Bradley

The affidavit from musician Moana Maniapoto includes news stories on the TPP.

A lawyer for some of the claimants, Kathy Ertel, said the Crown had alleged that the application for an urgent hearing was made too late.

But she said media reports showed information about the negotiations had been so sparse they weren't aware until the last minute that the agreement might be finalised, after US President Barack Obama was granted the authority to complete the trade pact.

"Because basically all of this has been undertaken in complete secrecy by the New Zealand government, so it was only through media leaks and media articles that we were able to get any idea of what the landscape was like."

The Crown has already declined to give an assurance that it won't commit to signing the agreement before the tribunal can decide if it will grant an urgent hearing.