Foreign Affairs Minister Simon Coveney has asked for a report into an image showing a gathering of officials in his department.
The picture emerged of staff drinking champagne during lockdown in June 2020, after Ireland won a seat on the United Nations Security Council.
At least 20 senior officials and staff are in the photo huddled together in an office at the department's headquarters at Iveagh House.
They can be seen drinking champagne without wearing masks or social distancing.
In a statement, the department says: "The department can confirm that a report has been requested by Minister Coveney and is expected before the end of the month."
The photograph was posted on Twitter by the then-secretary general of the department Niall Burgess - who is now Ireland's ambassador to France.
The investigation is set to be carried out by the new secretary-general, Joe Hackett.
Mr Coveney said last week he would be willing to go before the Oireachtas Foreign Affairs Committee to answer questions about the event.
He has previously said he did not attend any champagne celebration on the day that Ireland won its UN Security Council seat.