Mr Gaston said advice from the Auditor-General, published in 2007, notes the judicial test of bias as follows: "Is there a real danger of bias on the part of a member of the decision-making body, in the sense that they might unfairly regard with favour (or disfavour) the case of a party to the issue under consideration?"
Mr Gaston said the council was seeking to establish whether statements made in the media demonstrated bias and placed the council's decision-making at risk.
"Councillors can state a view. However, they are being advised that they should not be closed to any other views, and to keep an open mind when involved in the decision-making process."
Councillor Trevor Maxwell said be thought the four councillors who were members of the Rotorua Pro Democracy Society - Glenys Searancke, Rob Kent, Peter Bentley and Mike McVicker - had already prejudiced themselves and "had made no secret of their disapproval of the proposal".
"I would very much like to see what the legal opinion says before we sit down to make our final decisions.
"This group has made a lot of statements against the proposal. This to me is making up your mind before consultation has even begun.
"What will happen when those members sit down to hear their own submission during the decision making process?
"But, I'm also sure people on the society will question me and my position as a member of the iwi."
Councillor Charles Sturt said councillors who were members of the society were "guilty by association".
"I believe they have made up their minds already and seeking legal advice is correct.
"I hope common sense will prevail. But, those who have been questioned about their impartiality could also question our Te Arawa members about their impartiality.
"It's opening up a can of worms," he said.
Councillor and Rotorua Pro Democracy Society chairwoman Glenys Searancke could not be reached for comment. However, society secretary Reynold Macpherson said it was "silly business" and Mr Williams had overstepped his authority.
"We know from past experience that council officers have put out quite biased material and this is no different.
"The Te Arawa partnership plan has been pre-determined by the mayor and the three Te Arawa members of council whose determined efforts to get the proposal pushed through is the most explicit example of pre-determination we have seen."
Mr Macpherson said it was hypocritical for Mr Maxwell and others to say they themselves had not taken a predetermined position.
