Low fares airline EasyJet has launched a legal challenge against the merger between Air France and KLM.
It said it is taking the legal action on the grounds that the merger would substantially reduce consumer choice.
Europe's second largest budget airline has submitted an appeal to the Court of First Instance in Luxembourg, requesting it to annul the European Commission's clearance of the merger.
Easyjet has already complained about the allocation of take-off and landing slots at French airports, particularly Air France's dominance at Paris Orly airport.
The European Commission approved the merger last February.