Fianna Fáil has called on the Government to block Ryanair's bid to take over Aer Lingus.
The move followed Ryanair's shock announcement to the stock exchange that it was making a cash offer for the former State airline - which it values at €694m.
It is third attempted takeover of Aer Lingus by Ryanair since 2006.
A statement by Aer Lingus said it noted the announcement by Ryanair of its intention to make a third unsolicited offer for the company and it would make a statement in due course.
In the meantime, the statement urged Aer Lingus shareholders to take no action.
Ryanair is offering €1.30 per share, over 38% higher than the company’s current share price.
Previous bids foundered on competition issues, but Ryanair insists that circumstances have changed and the takeover should be approved this time.
The European Commission has said it has as yet received no notification from Ryanair or the Irish government on any takeover bid by Ryanair of Aer Lingus.
A spokesman said the previous decision by the European Commission competition authorities to block a takeover bid in 2006 was "well known".
Any new notification would be examined, a spokesman said.
However, Fianna Fáil transport spokesman Timmy Dooley said the Government should use its 25% stake to block Ryanair and sustain competition.
Minister for Transport Leo Varadkar said he would have to discuss it with his Cabinet colleagues.