IMPACT has asked the Data Protection Commissioner to investigate Aer Lingus after the company sent letters to cabin crew offering them another opportunity to agree to new rosters.
The letters were sent last night to staff who have been taken off the payroll over their protests at new rostering arrangements at the airline.
IMPACT claims the airline passed on personal details of staff with whom it is dispute to a courier company hired to deliver what the union describes as "threats" to staff.
IMPACT spokesperson Bernard Harbour said: "The company has a legal obligation to protect the data that it has on its staff and staff have a legal protection to their own security."