The Whanganui River Maori Trust Board says an iwi group claiming to have influence on a Treaty deed of settlement taking place this week, has no mandate to even comment on the matter.
The deed for the Whanganui River is to be signed with the Crown on Tuesday.
In March, tribal leaders initialled the deed at Parliament.
Of the 5000 Whanganui iwi members registered, 1500 voted, and about 97 percent of those who cast their ballots voted in favour of the deed, Te Ruruku Whakatupua.
However, the iwi group Tamahaki Incorporated Society says it has decided to reserve its decision on sign-off, claiming its signature is needed for the settlement to be full, final and binding.
The Whanganui River Maori Trust Board says that's not true and the group's decision has no effect on Tuesday's signing at Ranana Marae.