SIPTU tonight vowed to fight against 260 proposed job cuts at Shannon Airport.
Mr Michael Halpenny, National Industrial Secretary, claimed the Government had given commitments not to slash staff numbers at Dublin, Shannon or Cork.
"Any move to effect redundancy in Shannon would be completely contrary to these assurances," Mr Halpenny said. "We will be insisting that these protections are upheld in full and will strenuously oppose any attempt to depart from them.
"We also want to point out that it is very difficult to reconcile how the Shannon Airport Authority could announce on the one hand an increase in passenger numbers of 1.5 million in 2005 - on foot of the recent Ryanair deal - and on the other, to say there are too many staff employed at Shannon."
Under the State Airports Act 2004, three independent authorities were set up to run the country's three largest international airports. A number of conditions were included in the Bill including job security and terms and conditions of employment in the hope of protecting the future of hundreds of employees.
A spokeswoman for Shannon Airport said talks were set to get underway between unions and the airport authority on the proposed job cuts and to secure a viable future for Shannon.
"As part of the required improvement in Shannon's cost profile it is envisaged that the numbers of jobs directly involved in managing the airport will be reduced," she said. "It is expected that this will be achieved by means of a voluntary early retirement scheme."
The spokeswoman added it was hoped the cuts could lead to the development of a long-term profitable business at Shannon.
The Technical Engineering and Electrical Union, which represents the majority of craft workers at Dublin, Shannon and Cork airports, said the move proved Ireland could not sustain three international airports.
"Only by co-ordinating their activities can they serve the best interests of the economy and the taxpayer," he said. "This new proposal could spell the death knell of Shannon and seriously undermine the viability of Dublin. It has all the hallmarks of a business plan drawn up by Homer Simpson.
"Unfortunately it will impact on people living in the real world, not just at the three airports, but within the wider economy."