SIPTU President Jack O'Connor has described the decision to privatise Aer Lingus as dreadful and one the country would live to regret.
Mr O'Connor said if the concerns of his members regarding pay and job security were not addressed, his union would have no alternative but to resort to industrial action.
After a two-hour meeting with Transport Minister Martin Cullen, SIPTU representatives said they had heard nothing positive about the part privatisation of Aer Lingus.
The union's National Industrial secretary, Michael Halpenny, said SIPTU representatives had received no further comfort or concrete assurances on job security, pensions or outsourcing.
He said they had told the minister that they would have no alternative but to protect themselves with industrial action if any precipitative action were taken by the Government or the company.
It is expected that the Cabinet will make a final decision on the future of Aer Lingus tomorrow morning.
Speaking on RTÉ's The Week in Politics programme last night, the Minister for the Environment, Dick Roche, said Aer Lingus needed the investment generated from trading some of its shares if it were to prosper.
However, the Labour Party's Transport spokeswoman, Roisín Shortall, said Aer Lingus could continue to grow in State ownership.
She said as the national carrier, it was important to retain access to other parts of the world.
The Taoiseach, Bertie Ahern, has said the Government will seek certain protections for the customers and staff of Aer Lingus if it proceeds with a privatisation.
Mr Ahern said there were issues about pensions and staff conditions as well as the strategic importance of the airline which would have to be guaranteed.
