Data Protection Commissioner Helen Dixon is to be quizzed by TDs and senators about an alleged data breach at Independent News and Media (INM).
Ms Dixon has agreed to appear before the Oireachtas Communications Committee next week to discuss claims that data - including the emails of journalists, executives and other staff at the country's largest media publisher - may have been taken abroad and accessed by external companies in October 2014.
Her appearance will come a day after the High Court is scheduled to hear an application from the Office of the Director of Corporate Enforcement (ODCE), which wants High Court inspectors to investigate corporate governance matters at INM.
Green Party leader Eamon Ryan said the alleged data breach was "hugely concerning on a number of levels, regarding journalists' right to privacy, and the power of media owners to influence public debate".
"We want to question the DPC on the role her office has in addressing the data breach and the committee hearing next week should provide such an opportunity," he said.
"We know that the DPC considered reports of a data breach at INM in August 2017. We need to know what investigations took place on the back of that and why any investigation that did take place failed to uncover the true scale of the data breach."
Details of the suspected data breach emerged in an affidavit prepared by the ODCE.
It alleged that a so-called "data interrogation" was directed by former INM chairman Leslie Buckley and that invoices associated with it were paid by a company owned by INM's largest shareholder, Denis O'Brien.
Mr Buckley has claimed the data interrogation was part of a "cost-reduction exercise".
He says he intends to robustly defend his position.
Mr O'Brien has declined to comment.