Aer Lingus workers have returned to work after limited industrial action this morning in Dublin, Shannon and Cork.
Seven flights in and out of the airports were delayed and knock-on effects are expected.
Michael Halpenny, Siptu national secretary, claimed Aer Lingus had failed to commit to agreement on job security, on staff numbers and on terms and conditions of employment prior to privatisation.
He said a proposed pay rise for staff of 3 per cent had to be viewed in the light of increased pension contributions. The real increase would in fact be 1 per cent, he claimed.
A proposed profit-share scheme had also yet to be confirmed by the Department of Finance and by the Department of Transport, he said.
"It doesn't deliver money into anyone's pockets and it's a mechanism for ensuring the fact that the employee shareholding, which will be halved in proportion by any privatisation, will be at least brought up to its existing level. All it is is a mechanism for maintaining what the staff already have."
Mr Halpenny said his members had "no confidence" that Aer Lingus would seek to reach agreement on the issues prior to privatisation. It had also failed to take advantage of talks at the Labour Court, Mr Halpenny said.
Siptu says it is unacceptable that at any one time up to a quarter of staff in some parts of the company are "non-permanent". Mr Halpenny said the ratio of non-permanent to permanent staff in the cabin crew area was lower.
There was also "unfinished business" on the question of improvement in pension arrangements.
Mr Dermot Mannion, Aer Lingus chief, said clarity was required on what exactly the outstanding issues are before resorting to the Labour Court.
He said he did not accept the view that there was no value to the staff in the shares because what was on offer was a mechanism to buy additional shares with additional value.
Dermot Mannion, Aer Lingus
"The mechanism that will be used to pay for that is a target-based profit share scheme which is good for the staff going forward on the basis that if there is profit and we achieve a certain target, then that will be shared and will provide a mechanism to pay for the shares.
"I'm confident that we can deal with the pensions issue outside the Labour Court. I'm confident that we will deal with the issue of shares outside the Labour Court," Mr Mannion said.
He said that process was in train and meetings would take place with the Departments of Finance and Transport next week.
"This is an overall package deal. . . . I can only make this transaction happen as an overall package, and we can't allow a situation where individual elements of the package are taken out and negotiated in isolation."