Siptu workers at Aer Lingus today served the company with a protective strike notice which they say will be activated if plans to privatise the airline are implemented without consultation.
In a statement, the union said it would commence industrial action if the company proceeded "to privatise unilaterally and without prior agreement on the core issues of concern to union members".
Siptu's national industrial secretary Michael Halpenny said: "These issues include job security, commitments that there will be no compulsory redundancies or outsourcing, resolution of the pension issues and a number of unresolved long outstanding matters that arise from the business plan."
He said workers were also concerned that any floatation of the company does not dilute the employees' shareholding of 14.9 per cent.
"In deference to the considerable public support and goodwill that we have had to date for our campaign, and so as not to unduly inconvenience the travelling public over the Easter period, we are issuing our notice so as not to affect travelling arrangements during the holiday period.
Therefore the notice will only come into effect on expiry of two weeks' notice from today," he said.
The Government yesterday announced plans to float the airline on the Stock Exchange although it refused to specify an exact date.
Minister for Transport Martin Cullen said last night advisers would "immediately start work on the sale", but said it was not right for the Government to disclose a date for the actual sale.
He also said the Government planned to retain at least 25.1 per cent shareholding in the airline.
Siptu will articulate its concerns before the Joint Oireachtas Committee on Transport tomorrow which is holding its first hearing into the proposed sale of the airline.
Meanwhile Ryanair today claimed Siptu was refusing to use new scanning machines for the airline's web check-in servers.
The airline claims the service reduces the work load of staff and speeds up check-in reduces.
Ryanair chief executive Michael O'Leary said the union was "blocking progress at the Airport".