Airline Aer Lingus has urged shareholders to do nothing following a surprise bid from Ryanair to seize control.
The former Irish state-owned airline said it would release a full statement in due course in response to Michael O'Leary's third bid to buy out the airline.
Ryanair already owns 30% of Aer Lingus and Mr O'Leary's fresh offer, which emerged on Tuesday night, would value it at 694 million euro (£560 million).
The Irish government still holds a 25% stake in the airline, which it has been hoping to sell as a state asset following an agreement with its bailout masters the Troika.
If Ryanair's bid is accepted, its offer of 1.30 euro per share would result in a 175 million euro windfall for the Irish Exchequer.
An Aer Lingus spokesman said: "The board of Aer Lingus Group plc notes the announcement by Ryanair Holdings of its intention to make a third unsolicited offer for 100% of the entire issued, and to be issued, share capital of Aer Lingus.
"Aer Lingus will make a statement in due course. In the meantime, Aer Lingus shareholders are urged to take no action."
The Irish government has not commented on the development. It is understood Transport Minister Leo Varadkar is to discuss the issue with his colleagues in Cabinet before issuing a statement.
The government announced plans earlier in the year to sell 3 billion euro of state assets, including parts of energy suppliers Bord Gais and ESB Electric Ireland. It also identified its remaining 25% stake in Aer Lingus as a non-strategic asset and revealed it would sell its share when the best offer came along.
Irish opposition party Fianna Fail has appealed to the Government to use its stake in Aer Lingus to block the buy-out. Transport spokesman Timmy Dooley said a consolidation of the two airlines would result in reduced competition, increased fares and less choice. He said a potential hike in fares in particular would be bad for the country's economic recovery and efforts to boost exports.
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