Institutional Shareholder Services is the latest organisation urging Abano Healthcare shareholders to ignore moves to unseat chairman Trevor Janes.
The organisation advises fund managers and is recommending Abano's shareholders vote against removing Mr Janes.
On Friday, major shareholders Peter Hutson and James Reeves applied to the High Court to delay a special meeting they requisitioned to vote on ousting Mr Janes and which has been set for 13 June.
Affidavits from both men, who own 18.6 percent of Abano between them, acknowledge Abano has met the statutory requirements in setting the meeting's date.
But after weeks of saying that Abano was seeking to delay the meeting, the pair now say they have not been given enough time to communicate with other shareholders.
The Shareholders' Association last week sent its own letter to Abano's shareholders recommending they vote against Mr Janes' removal
Association chairman John Hawkins said his organisation was concerned about the move to try to delay the meeting.
"We think it's an attempt to confuse and mix up the situation. There is no reason why the meeting should be delayed," Mr Hawkins said.
"There's been plenty of information out in the press, and I note that Mr Hutson and Mr Reeves could have sent out their information to shareholders at the time ... with the information that went from the company.
"Apparently they chose not to. For them to say they haven't had time is pretty misleading, really."
Mr Hawkins encouraged shareholders to read the Shareholders' Association letter in its entirety to get its full perspective.
An Abano spokesperson said the company could see no reason to change the legally valid meeting date.
Mr Hutson and Mr Reeves declined to be interviewed by Radio New Zealand.