Foreign Affairs Minister Simon Coveney is to be called before an Oireachtas committee to answer questions about the 2020 ‘champagne-gate’ party in his department.
The foreign affairs committee has agreed to ask Mr Coveney to appear before it and provide testimony.
At a private meeting of the committee, several members took issue with secretary-general Joe Hackett being tasked with overseeing the inquiry into a photograph posted online by his predecessor, Niall Burgess.
The photograph showed around 20 civil servants huddled together, unmasked, drinking champagne, while strict lockdown restrictions were still in place.
Sources say members raised concerns about Mr Hackett investigating his own departmental colleagues.
Fianna Fáil senator Diarmuid Wilson, independent senator Gerard Craughwell, Social Democrats TD Gary Gannon, and independent TD Cathal Berry all raised concerns about the investigation being carried out by the current secretary-general rather than someone outside the department.
Mr Flanagan agreed to highlight the issue in a letter to the minister.
The committee has agreed to write to Mr Coveney asking for the terms of reference, scope of the investigation, and the timeframe for its completion.
Concerns will be expressed in the letter about the investigation being headed up by the secretary-general of the department.
The committee is also likely to explore why the foreign affairs minister did not reveal the existence of the investigation in an interview on Friday.
His party leader, Tánaiste Leo Varadkar, stumbled during a radio interview when asked about the party.
A spokesperson for the Tánaiste has since said that Mr Varadkar was aware an investigation was under consideration but he did not know it had been decided.
Sinn Féin has accused Mr Coveney of blindsiding his colleagues by announcing the probe on Sunday evening.
Foreign affairs spokesperson John Brady said the minister had initially ruled out an investigation because he trusted his colleagues.
Members called for Mr Burgess, assistant secretary-general Brendan Rodgers, and Global Ireland director-general John Concannon to come before the committee.
Mr Brady said the deafening silence from Mr Coveney when the controversy first emerged has exacerbated the situation.
He also raised questions about the minister’s changing stance on the need for an investigation into the party.