Aer Rianta could be forced immediately by international banks to pay back nearly €500 million worth of loans and bonds, the company has warned the Government.
In a letter to the Department of Transport on June 30th, the Aer Rianta's chief executive, Ms Margaret Sweeney, said the actions could leave the company insolvent.
Lenders' approval should be got before the Minister for Transport, Mr Brennan, makes any attempt to break up the company, argued the letter, which was revealed by RTÉ News.
Her warnings came as the former minister for public enterprise, Ms Mary O'Rourke, warned that the Government's legislation was premature and poorly drafted.
In her letter, Ms Sweeney said: "It appears that enactment and implementation of the Bill will result in an event of default occurring under the group's funding arrangements."
The warning came after two legal firms had examined the impact of the legislation, which is due to be passed by the Seanad this week.
Both Matheson Ormsby Prentice and Arthur Cox & Co believe bond trustees will delay approving the restructuring until they have met with bondholders, she said. "Ultimately, however, a decision as to whether an event of default has occurred under this heading is a matter for the bond trustees," she went on.
Under the terms of its agreement with banks, Aer Rianta faces demands for early loan repayments if over €32 million of debt is "declared due prematurely by reason on default".
"Both lawyers have advised that waivers will be required from some bondholders and possibly from the bond trustees," she wrote.
"Clearly, Aer Rianta would not want to put itself or find itself put into default with its banks or bondholders. It would be important that we have the confidence of the banks and possibly bondholders will provide the necessary waiver before attempts to implement restructuring are made."
Refinancing would be costly and might not be available, she warned: "In such circumstances, the company would be likely to find itself in an insolvent position.
She added: "Aer Rianta wants to ensure that no action is taken which could constitute an event of default prior to discussions having taken place with lenders and relevant consents or waivers having been agreed."
