Budget airline Ryanair has mounted a fresh bid to seize control of its rival Aer Lingus by tabling an offer valuing the company at €694m(£559.6m).
Ryanair, which owns a 29.8% stake in its rival, aims to boost the Aer Lingus' passenger numbers by 4.5 million to 14 million over the next five years by forming "one strong Irish airline" to compete with major European players.
A previous takeover attempt in 2006 was rejected by regulators but Ryanair said consolidation and the economic downturn had since left Aer Lingus "exposed as a small and uncompetitive airline".
The Republic's opposition party, Fianna Fail, called on the Irish government to use its shareholding in Aer Lingus to prevent Ryanair from taking control of the airline.
Transport spokesperson Timmy Dooley said: "The existence of Ryanair and Aer Lingus as separate competing entities has transformed our tourism and business connectivity.
"Any material change to the separate status of these airlines would inevitably lead to reduced competition, increased fares and less choice.
"Ryanair has provided good competition in the Irish market for many years.
"Its business model has resulted in cheaper fares and helped grow the Irish tourism market.
"What we don't want is to see a reversal of this position."
The fresh bid for Aer Lingus comes as Ryanair faces being forced to sell its stake in the company after the Office for Fair Trading referred its holding to the Competition Commission.
But Ryanair said BA's recent takeover of British Midland was the latest in a series of consolidations. The European industry was "inexorably" moving towards being controlled by five large airlines led by Air France, BA, easyJet, Lufthansa and itself, it argued.
Aer Lingus currently operates out of Belfast International. It flies to Alicante, Barcelona, Faro, Gran Canaria, Lanzarote, London Heathrow, Malaga and Tenerife. However, it could be set to offer flights from George Best Airport to Heathrow, Gatwick, Edinburgh, Manchester, Birmingham and Glasgow airports - if it switches its operations as widely expected.
Ryanair departed from Belfast City in 2010 blaming its decision on the delays in delivering the controversial runway extension.