SIPTU has indicated that it will serve industrial action notice on airport operator Aer Rianta tomorrow morning.
The move by Ireland's largest union gives the Aer Rianta seven days notice of any industrial action SIPTU may recommend.
The aviation branch of the union is set to consider its option further but has not confirm for definite whether any industrial action would be taken after the seven days lapse.
Earlier today, the IMPACT union which represents middle management returned a ballot in favour of strike action.
This follows the Minister for Transport Seamus Brennan's letter to airport employees stating that the Government's decision to break-up Aer Rianta was final and that his Department would implement the decision as quickly as time allowed.