Egyptian Ambassador Soha Gendi has declined an invitation to appear before an Oireachtas committee to discuss the case of Ibrahim Halawa.
The Dublin man has been in prison in Egypt for over 1,000 days, having his trial postponed 14 times.
Ambassador Gendi has written a letter to Ceann Comhairle Seán Ó Fearghaíl in which she said she will not appear before the Oireachtas Foreign Affairs Committee.
Ms Gendi also contacted the committee directly to indicate her intention not to attend.
Earlier this month, both houses of the Oireachtas passed cross-party motions calling for Mr Halawa's release.
The motions also called on Ms Gendi to appear before the committee to address concerns over delays in the young Dubliner's trial and to request her to convey to the authorities in Egypt that he should be released as soon as possible.
The Foreign Affairs Committee, which is chaired by Fianna Fáil TD Brendan Smith, held its first meeting this morning.
It is understood that the ambassador's decision not to attend the committee was discussed in private session at the start of this morning's meeting.
It is also understood that plans for a parliamentary delegation to travel to Egypt to raise Mr Halawa's case are still in train.
Representatives from Oxfam and Dochas appeared before the committee this morning for a discussion on migration.
The committee has adjourned until 15 September.
Oireachtas Foreign Affairs Committee member Senator Mark Daly said "it's disappointing that the Egyptian ambassador would not appear before the committee.
"The Taoiseach now needs to do what the Australian Prime Minister did and seek a presidential decree.
"That successfully secured the release of Peter Greste."
Australian Mr Greste was one of three Al Jazeera journalists arrested and jailed in Egypt in 2014 on terrorism charges.
He shared a prison cell with Mr Halawa.
Senator Daly called on the Taoiseach to act immediately. He added that the Foreign Affairs Committee has now invited Ibrahim Halawa's legal team before them at its next meeting on 15 September.
"We have also invited in the officials from the Department of Foreign Affairs. We will ask them to explain why they have not followed the example of the Australian government who successfully secured the release of their citizen following intense diplomatic lobbying," said the Fianna Fáil senator.
Speaking earlier this month, the Minister for Foreign Affairs outlined that the Government formerly supported an application made by Mr Halawa's legal team in 2015 for his return to Ireland under Presidential Decree 140.
He said the Government will continue to offer all appropriate supports to the efforts of Mr Halawa's lawyers to secure his release.
