The daa, which runs Dublin Airport, was prepared to pay "whatever is required" as the Defence Forces said they were being asked to cross a "Rubicon of sorts" in helping with the security delays that have dogged the airport.
The military was put on standby early last month to step in to ease lengthy queues at Dublin Airport and avoid further "reputational damage" from weeks of queuing chaos.
In correspondence with their parent department, the Defence Forces said they would need as much "lead in time as possible" to get prepared for airport duties.
An email from Major General Anthony McKenna on 23 June said: "I think that this point is required to be made forcefully before we find ourselves committed and deployed underprepared in an uncertain task."
In discussions, Maj Gen McKenna, the Defence Forces' Deputy Chief of Staff for Operations, said if they were put on standby, they needed immediate engagement with the daa which runs Dublin Airport.
He said they would need to know what duties were involved, what manpower was required, and how rostering would work.
Maj Gen McKenna wrote: "There are other equally complicated issues associated with this potential task with which you are well familiar.
"However, putting the Army/Defence Forces on standby is a Rubicon of sorts, which would require definitive operational and training responses."
An earlier email between the Department of Transport and Department of Defence said "higher level contacts" were already taking place between ministers.
It said they now needed to "deepen consideration" of putting the military on standby pending clarification of the legal situation.
A proposal said the Defence Forces would be put on standby but be "capable of activation at very short notice".
The email said rapid training and certification of army personnel would be required and the operation would be subject to inspection by the Irish Aviation Authority.
It said military support would allow daa to free up 100 staff that could be redeployed into the airport terminals to help with lengthy queues.
The email added: "The daa will pay whatever is required. It is understood that the army is already a 'regulated agent and known consignor' so that [the] Irish Aviation Authority has already recognised army training for certain security purposes."
Army representative organisations also raised queries about how the standby arrangement would work, particularly around pay and working time.
A letter from RACO (Representative Association of Commissioned Officers) asked if rosters would involve breaches of working time legislation and how members would be compensated.
Their letter asked if personnel would be paid a special maintenance of essential services allowance, the same as had applied during the Covid-19 pandemic.
General Secretary Commandant Conor King also asked: "Where will personnel be accommodated, and what rationing or subsistence arrangements will be in place?"
PDFORRA, which represents enlisted personnel, also raised concerns over its members being asked to work hours "beyond limits" provided for under law.
An email from it said: "It must be remembered that these duties are going to be undertaken by units that are already under strength."
A later letter warned that a situation where daa staff were being paid shift allowances and overtime payments could lead to an "impact on morale" if appropriate payments were not made to members of the Defence Forces.
In an email between the department and the Defence Forces in late June, it said the arrangement would involve provision of up to 100 military personnel to provide screening at four entry points to Dublin Airport.
It said a special accounting code would be created so that all services provided to the daa would be billed directly to them.
Asked about the records they released under FOI, the Department of Defence said it had nothing further to add to their contents.
