Siptu is considering a letter from Aer Lingus that warns of staff suspensions unless there is co-operation with new working structures.
The airline is demanding that staff assist in training new employees recruited on lower terms and conditions.
Aer Lingus is seeking to reduce annual leave, change shift allowance payments, reduce overtime, and introduce more flexible working hours and practices. It also wants to cut time off in lieu for working bank holidays.
The company has advised customers that disruption to travel on Wednesday, Thursday or Friday of next week is a possibility.
Siptu's 1,800 members at Aer Lingus are preparing to withdraw their labour from March 1st if the airline does not back down on plans to introduce new contracts for existing staff.
The trade union has formed an 11-member disputes committee comprising shop stewards at Dublin, Cork and Shannon airports, and union officials.
It is understood that the shop stewards will meet next Monday evening to formalise their strike plans.
"A withdrawal of labour is being planned," said a senior Siptu source. "The disputes committee will formalise arrangements for the extent and timing of our action next week."
Aer Lingus' Dermot Mannion said: "Siptu is well aware that if the current uncompetitive work practices are not addressed now, the staff costs per passenger will continue to rise and erode our ability to maintain Aer Lingus's growth as an independent and profitable company."
The carrier is claiming that Siptu is only prepared to discuss the setting of the deadline but is refusing to engage "on the real commercial issues" and instead "seems to favour the unnecessary interruption of service to passengers as an instrument to make its case".
Unions have not given details of the planned industrial action and have yet to announce a date for any strike.
However, the Aer Lingus Craft Group of Trade Unions (ALCGTU), which represents about 200 Aer Lingus staff, has said a strike is almost certain.