Businessman Denis O'Brien has accused Ireland's director of corporate enforcement of leaking details of his application to have inspectors appointed to Independent News and Media.
The High Court has been asked to decide whether to probe governance arrangements at the media group, which owns the Irish Independent and Belfast Telegraph, but has delayed making a decision while further legal issues are discussed.
Major INM shareholder Mr O'Brien wrote to director Ian Drennan saying the alleged leaks had damaged his reputation.
His letter, read out in court, said: "I hold you fully and personally responsible for all such failures and breaches."
A lawyer for the director, Neil Steen SC, said: "We are reasonably satisfied that those allegations are unfounded."
There is a compelling public interest in appointing inspectors to investigate Independent News and Media data use, he told the court.
Mr Steen said there were significant concerns about use of the material by people outside the Republic's largest media group.
He said they surrounded the removal of data from INM to a third company outside the jurisdiction "resulting in INM data being interrogated".
Mr Steen added: "There remains significant concerns as to the purpose of the data interrogation, accessible by a range of individuals."
He said some of those individuals were found to have links to Mr O'Brien, the successful businessman and largest shareholder at INM.
It follows a data breach within the firm in 2014 involving several people including some of its own journalists.
Mr O'Brien wrote to the director of enforcement about confidential information emerging into the public domain which he said was damaging his reputation.
The decision of the director to bring the legal proceedings is due to go to judicial review next month and that will determine whether to proceed on the substantive case, judge Mr Justice Peter Kelly said.
- Press Association