"If [Tuhoronuku] decided not to adopt the Maranga Mai recommendations in full the Crown would quickly reassess its decision to recognise '[Tuhoronuku's] mandate'," said Mr Finlayson.
The Maranga Mai report was produced by the Ngapuhi Engagement group - a tripartite group comprising the Crown, Te Kotahitanga and Tuhoronuku - which was established to address issues raised in the Waitangi Tribunal's report into the Ngapuhi Mandate, which found the structures and processes of Tuhoronuku undermined hapu sovereignty.
Tuhoronuku board trustees Erin Shanks, Bill Hori and Moana Tuwhare put forward a resolution urging the board to indicate their position by September 16.
Mr Shanks said he was concerned the negotiations would be delayed.
"Effectively that would put the process back, potentially years. We know there is an election next year and I suppose the question remains whether or not this has become a toxic thing for the Government." he said.
Mr Shanks said Mr Sadler had set a meeting for September 16 but rescinded that after receiving the letter from Mr Finlayson. But Mr Sadler said that was not true as he had an appointment in Wellington on September 16.
He said the reason for not having a meeting on Maranga Mai before September 20 was because of a lack of funding and availability as some trustees have to travel from Wellington and Auckland.
"There are a number of trustees who weren't available and it is such an important event and important issues they need to be discussed face to face."
In a letter to Mr Finlayson, Mr Sadler said there were outstanding issues needing to be discussed - urban representation, kuia/kaumatua representation, roles of Te Hononga Iti (a hapu decision making group) and Te Kotahitanga wanting to have equal rights and representation in the transition process.
Ms Tuwhare said the board unanimously passed a resolution accepting the draft Maranga Mai report and said board members were confused why those issues needed to be revisited.
"The urban representation issue for all intents and purposes was recommended by the hapu to determine for themselves ... We support there being two options for separate representation and hapu taking it on."
Ms Tuwhare agreed the mandate will be at risk if Maranga Mai is not adopted in full.
"Our people are fed up ... Many of hapu groups they never supported Tuhoronuku in the first place they're going to sit back and say 'I told you'."