Independent News & Media (IN&M) has described businessman Denis O'Brien - who holds a 22 per cent stake in the company - as a "dissident shareholder".
In a separate statement to its annual results released this morning, IN&M said that Mr O'Brien's "comments and actions regarding IN&M, its board, management, strategy and governance, are designed to destabilise".
It alleged that by consistently voicing disagreement with company strategy while continuing to buy shares Mr O'Brien is not acting in the best interests of all stakeholders.
The statement quotes from a letter sent by Mr O'Brien to the company almost five years ago in which he alleges that newspapers within the IN&M group had "spent the last seven years trying to destroy my reputation" and added that he was "waiting for the appropriate time to rectify the damage".
It also criticised Mr O'Brien for his commissioning and issuance of a report into the business and governance of IN&M.
IN&M claimed today that the document was "without merit" and said it was compiled without contacts with IN&M's management team or board of directors.
The statement concludes by alleging that Mr O'Brien's criticisms of IN&M's strategy would "appear to be borne out of self-interest, with no proper regard whatsoever for the company, its assets, [or] its stakeholders".