Aer Lingus faces losses of up to £10 million as a result of the series of three one-day pay strikes by the company's 3,000 clerical staff which began on Friday.
The national airline's entire fleet was grounded when pickets were placed on Dublin, Cork and Shannon airports, with two more stoppages due over the next fortnight.
SIPTU says the clerical, catering, cleaning and ground handling staff want parity with 1,350 cabin staff, the majority of them IMPACT members, who completed a new pay deal with the company in January.
Aer Lingus says that to concede so-called catch-up claims would be to compromise the competitiveness of the company.
Both sides say they are hoping for third-party intervention before Friday next, when the next strike action is planned.
