Ryanair has submitted its appeal to the European Court of First Instance in Luxembourg against the EU Commission's decision to stop its takeover of Aer Lingus.
Ryanair was required to seek approval for clearance of the takeover deal from the European Commission.
However, following an eight-month investigation, the Commission blocked the merger.
"This merger, which accounts for less than 5 per cent of the EU air transport market, was clearly pro-competition and would have been the first merger in history to guarantee fare reductions," said Ryanair's head of regulatory affairs Jim Callaghan.
"The Commission made several manifest errors in its assessment of the merger and ignored evidence from Ryanair demonstrating the numerous benefits that the merger would bring to consumers and increased competition with the high fares mega carriers."
He said that Ryanair had also offered unprecedented commitments to the Commission to address any possible competition concerns.
Aer Lingus said that it was "in no doubt that the appeal announced today will fail, and Aer Lingus will assist the Commission in upholding the decision before the court."
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