The organisation representing Irish soldiers, PDFORRA, has formally applied to affiliate to the Irish Congress of Trade Unions, RTÉ News has confirmed.
Such a move has previously been strongly resisted by the government.
Traditionally the Defence Forces bodies - PDFORRA, which represents enlisted personnel, and RACO, which represents officers across the Defence Forces - were barred from going on strike, joining Congress, or fully participating in public service pay negotiations.
There were Government concerns that if they were permitted to affiliate to Congress, the Defence Forces could be compromised if called upon to plug gaps caused by a strike in another union in an essential service.
In recent years, unions have tended to supply their own emergency cover rather than relying on third parties.
Section 2 of the Defence (Amendment) Act 1990 states that Defence Forces representative bodies cannot join Congress without the permission of the Minister of Defence.
This was based on concerns that affiliation could affect the operational effectiveness of the armed forces and military discipline - and to avoid them being destabilised by protest movements within organisations such as ICTU.
The Government also opposed the right to strike for military personnel as a strike could disrupt vital operations or threaten national security.
Some years ago, PDFORRA won a case against the government at the Council of Europe Committee on Social Rights, which found that members of the Defence Forces should have union rights - including the right to affiliate to Congress - but not the right to strike.
PDFORRA argued that that the Government ban on joining Congress violated the European Social Charter in a number of respects.
The Committee found that the body representing 7,000 enlisted personnel did not have sufficient access to pay agreement discussions.
RACO, which represents over 1,000 officers, was not a party to the PDFORRA case, and has not sought the right to ICTU membership.
Congress sources confirmed that the PDFORRA application had been received, and that General Secretary Patricia King will present a report to the next Executive Council meeting later this month.
The Minister for Defence, Paul Kehoe, told RTÉ News he was aware of PDFORRA's desire to affiliate with ICTU.
He said that on his direction, there is ongoing engagement between ICTU and the Department of Defence.
He also acknowledged, in considering this matter, the need to carefully consider the implications of such a move.
The Department of Public Expenditure and Reform which oversees public service pay negotiations said it had no comment at this time.
The Department of Justice said this was a matter for the Department of Defence.
In the PDFORRA letter applying for affiliation on 31 July, General Secretary Ger Guinan said that while the organisation recognises the fears of Government, "... it is an honest belief held by PDFORRA that any association with ICTU will have no impact, in terms of undermining morale or the Esprit de Corps. These traits are necessary and exist in all armed forces - unionised or not."
He noted that the organisation had been campaigning hard for the grant of permission from the line minister, and outlines the case taken to the European Council's Committee of Social Rights.
He stated that "PDFORRA has at all times sought to progress our case for Associate status to ICTU through agreed procedures and in a manner that is transparent, lawful and in a manner that acknowledges, and assuages to the greatest possible extent any rational fears that interested parties may have".
He also stated: "You may consider it necessary to notify the Minister ... of PDFORRA's willingness ot have imposed upon it any caveats to membership of ICTU which he may deem necessary, reasonable and appropriate."
He continued: "... the Association is willing if it is believed necessary ... to enshrine within our Constitution that our Association will not call for, or support any strike action by serving members, albeing that the foregoing is believed to be wholly unnecessary and superfluous given current regulations."