Aer Lingus was forced to cancel two US services today in a row with cabin crew over a change to working hours.
The airline said staff refused to operate under new rosters and the flights between Dublin and Boston had to be pulled from schedules.
Aer Lingus said about 30 cabin crew employees refused to co-operate with the changes.
"The sole responsibility for these cancellations, and the corresponding disruption to customers' travel plans, lies with the Impact trade union which continues to take industrial action despite 15 months of negotiation, agreement, clarification, conciliation and binding arbitration," the airline said.
Disrupted passengers were being re-accommodated on flights to New York later today or Boston tomorrow, the airline said.
Aer Lingus said it had managed to avoid disruption until now.
Management wrote to cabin crew last week detailing new rosters to meet the commitment to 850 flying hours a year previously agreed with staff.