The Friends of Matapouri group is backing court action by Maori landowners in a bid to stop a coastal subdivision.
The land is at the north end of Matapouri Beach, on the east coast north of Whangarei.
Te Whanau o Rangi Whakaahu say they sold the Otito Block, to the Government in 1970 as a scenic reserve, in the belief that reserve status would safeguard it for all time.
However, they say part of the land was wrongly included in a freehold title by private survey 10 years ago.
A condition of sale was that a neighbour who had built a house there, would get a lifetime lease and the house would be removed when she died.
But the then-Lands Department never got around to drawing up a tenancy agreement.
The neighbour's descendants, the Ringer family, had the block re-surveyed in 1999 and that survey set the boundary well north of where the hapu says it is.
Te Whanau o Rangi Whakaahu lodged affidavits in the High Court in Whangarei on Thursday asking for the land to be returned to the Crown. The suit is backed by The Friends of Matapouri.
However, the Ringers say they have clear legal title, confirmed by the Surveyor General - after a survey that DoC agreed to abide by.