In it they say they want the merger process as it is to be stopped and instead request the two institutions to "develop a meaningful proposal document and to openly consult with their communities".
Mrs Chadwick said she waited for the business case to be analysed before stating her views but now believed there was no support for the proposed merger. The letter was sent on Thursday after she attended a public meeting on the matter on Wednesday night, along with the council's chief executive and other councillors.
"We were unhappy with our own analysis of the business case," she said.
The council was going to make its own submission to the merger consultation but its opinion was affirmed at the public meeting.
"That's when the community clearly expressed their opinions. Sir Toby has been concerned. We thought the business case might answer our concerns but it raised more questions."
She said a meeting with Waiariki chief executive Margaret Noble and Waiariki chairman Graeme Nahkies left her "still unconvinced".
"The public meeting was a clear indicator for me.
"If the public had felt [the merger] was a good thing I think we would have just put in our own submission but there was no one there, other than four of the Waiariki councillors, who said it was a good thing. There are clearly some different views and I think it needs more work."
The letter mentions the proposal "fails to consider aspects of crucial interest to the Rotorua and neighbouring communities", and ignores the "huge differences which exist across the Bay of Plenty".
"The name and the land Waiariki sits on was gifted by Te Arawa and the facility is seen as a crucial part of the social fabric of Rotorua."
The letter's authors also said they believed there had been little attempt to engage the community in meaningful dialogue.
Following the public meeting Mr Nahkies said the business case followed "the Government's 'better business case' template and is aimed at providing the information that the minister would expect to see when considering the proposal".
"We believe combining our two organisations opens up some significant opportunities for the people of the region, including Rotorua."
Tertiary Education, Skills and Employment Minister Steven Joyce said there was a formal process he had to follow when a merger proposal for public tertiary institutions was put to him.
"That is the process we are currently going through. I welcome submissions from all parties including the Mayor and local iwi and I will consider all submissions thoughtfully."
He said he understood discussions about a possible merger had been going on for much of the year.
"It will be important to get a resolution one way or other in a timely fashion so that the two institutions and their staff have clarity about the future. I therefore intend to make a decision once I have received all the submissions and considered them carefully."
Waiariki merger
* Protest march at Waiariki at noon today, organised by students.
* Letter sent to Minister Steven Joyce by Rotorua Mayor Steve Chadwick and co-signed by Sir Toby Curtis and Grahame Hall urging for the process to be stopped.
* Submissions open until tomorrow.
