The council is due to consider receiving and agreeing to a modified statement of intent (SOI) which directs its Queenstown Airport Corporation.
In a letter sent to the council yesterday, Wanaka Stakeholders Group chairman Michael Ross said his group "put QLDC on notice of what we consider to be the unlawfulness and unreasonableness of actions and decisions to date in relation to existing Wanaka Airport".
"Any decision by council to agree to the modified SOI will ... be unlawful - in breach of the Local Government Act 2002".
Mr Ross said agreeing to the modified statement of intent would confirm "earlier unlawful decisions and actions" over the transfer of the airport from the council to the QAC.
Also, it would have the effect of "agreeing to decisions and plans of QAC to develop existing Wanaka Airport into a physically expanded and materially different airport".
He referred to sections 76, 77, 78 and 82 of the Local Government Act 2002.
"The SOI process followed by QLDC and QAC is in breach of these provisions," he said.
The sections deal with local authority decision-making processes, in particular the need to "identify all reasonably practicable options" and consider "the views and preferences" of those affected.
Mr Ross said one option was for a new site for a Lakes District Airport to be investigated, but Mayor Jim Boult last week ruled that option out.
The stakeholders group has 2500 members and opposes QAC plans to expand Wanaka Airport to allow commercial jets.
In a second letter to the council, John Hilhorst, a member of the Flightpath 2050 group which is opposed to expansion of Queenstown Airport, questioned the validity of Mr Boult's statement before the last council meeting, in which he outlined modifications to the statement of intent, which included economic and social impact assessments being done.
"The speech was not a resolution of council, nor from any sub-committee of council; its legal standing in the SOI process is questionable."
A spokesman for the QLDC indicated a response to Mr Ross' letter was likely early next week.
The extraordinary meeting is at 10am on Monday.
