Ryanair has asked EU antitrust regulators to approve the €694m (£535m) takeover bid - its third - for the former state carrier in what could be an uphill battle after an EU veto against a previous offer.
Aer Lingus wrote to its shareholders at the end of July outlining why it recommended rejection of the offer and said today it had heard nothing from Ryanair to change that stance.
"No new information has been provided by Ryanair in relation to the offer and the board re-affirms its recommendation that shareholders should reject the offer," Aer Lingus said in a statement.
"Ryanair's offer is not in the interests of shareholders, fundamentally undervalues the business and is likely once more to be prohibited by the EC," it said.
The EC, which acts as EU competition watchdog, said it would decide by 29 August whether to clear the deal.