Aer Lingus will face further industrial action if privatisation of the airline proceeds in the absence of an agreement on workers' terms and conditions, Siptu warned yesterday.
Several hundred of the union's members, employed by Aer Lingus at Dublin, Cork and Shannon airports, took part in a stoppage yesterday of just over an hour.
The action, which began shortly before 10am, caused some flight delays, but Aer Lingus said services were returning to normal by early afternoon.
Further talks are planned next week to address outstanding issues between management and unions arising from the planned part-privatisation of the airline.
Addressing workers who took part in the protest at Dublin airport, Siptu Aer Lingus branch organiser Christy McQuillan said further protests would take place only if "absolutely necessary".
"But I must leave you on alert that we may have to have further action to protect our interests," he said.
Siptu is fighting the privatisation of Aer Lingus on two fronts. It is opposed to the move in principle, but is also seeking measures to protect workers' pay and conditions in the event of privatisation going ahead.
The union's president, Jack O'Connor, who also addressed workers at the Dublin protest, said the large turnout had "nailed the lie" that the union's stance was an ideological one orchestrated by its leadership.
"I was here today as well to nail the other lie that has been circulated, to the effect that there is some kind of nod-and-wink or tacit understanding between the leadership of the union and the Government to let this [ privatisation] go ahead.
"I thought it was important that I would come out here and make it clear that nothing of the kind has happened," he said.
Mr O'Connor said yesterday's protests were not part of the campaign to prevent the privatisation of the airline from taking place.
"The actual industrial action is about dealing with the consequences of [ privatisation], but we're not giving up on the campaign to prevent it from happening."
Siptu met management of the airline on Wednesday and says it has four outstanding concerns, in the areas of job security, pensions, pay and the workers' shareholding in the company.
Aer Lingus chief executive Dermot Mannion said yesterday that significant progress was being made in talks with Siptu and other unions, which were continuing.
Mr Mannion and other members of management at the airline spent time "on the ground" yesterday meeting passengers discommoded by the industrial action.
A total of six flights were directly affected. An outbound flight, from Dublin to New York, was delayed by more than an hour, while passengers on five inbound flights experienced delays in receiving their luggage.
There were knock-on delays to flights but by 2pm these had been reduced to between 10 and 15 minutes, an Aer Lingus spokeswoman said.