Almost 500 Aer Lingus pilots who are members of the Irish Airline Pilots' Association are to stage a 48-hour strike next week.
The industrial action is being taken over the pay and conditions of pilots who will be employed at Belfast International airport.
The union says the new pilots will have less favourable terms and conditions of employment.
Union officials say pilots would not be eligible for the existing pension scheme and they could not avail of existing agreements.
The strike is due to take place next Tuesday and Wednesday and all Aer Lingus routes will be affected for 48 hours.
The airline, which is seeking to employ 25 to 30 pilots for its Belfast base, has described the decision as bitterly disappointing, accusing the pilots of attacking customers.
A spokesperson for the company also said the action directly ignores the recommendations of both the Labour Court and the Flynn report earlier this year that the company should be allowed to proceed with opening bases outside the Republic.
