Aer Lingus has urged shareholders to do nothing following a surprise bid from Ryanair to seize control.
The Irish former 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, the Press Association reported.
Ryanair already owns 30% of Aer Lingus and Mr O'Leary's fresh offer, which emerged on Tuesday, would value it at €694 million (£560m).
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 (£1.05) per share would result in a €175m euro (£141m) 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.
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".
Ireland'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."