Abano major shareholder Peter Hutson, who was behind a failed take-over attempt last year, is calling for chairman Trevor Janes to resign.
Mr Hutson, a former director, and fellow shareholder James Reeves, who together own 19 percent of Abano, are also criticising the company's dental strategy and want it to immediately cease buying dental practices.
They are critical of the company's performance and have commissioned their own valuation from KordaMentha which says Abano's shares are worth $6.46 each, about the current share price.
That's much less than the $8.30 to $10.05 per share valuation Abano commissioned from Grant Samuel last year and which Grant Samuel affirmed last month.
Milford Asset Management executive director Brian Gaynor, who is one of Abano's institutional shareholders, said Mr Hutson does not have his support.
He said they have been trying to get the support of institutional shareholders over the last month, but he doesn't think they have got the support of many, if any at all.
Mr Gaynor said he doubts they will be successful in getting Mr Janes to resign as chairman.
He said there could be some merit in slowing the dental acquisitions and running the existing dental businesses harder but that the dental strategy should be tweaked, not abandoned.
In a statement, Abano's board said it sees no merit in Mr Hutson's criticism and that it unanimously supports Trevor Janes remaining as chairman.