Greek carrier Olympic Air is withdrawing services from London to Athens and Thessaloniki from the end of the month.
Flights to Paris, Brussels and Vienna are also being suspended.
The London flights are being dropped from March 27.
Olympic says it plans to “maintain or expand” international services to Amsterdam, Belgrade, Bucharest, Cairo, Istanbul, Larnaca, Sofia and Tirana.
The moves come as the airline works on an appeal against a European Commission decision to block a planned merger with Aegean Airlines.
Airline president John Karakadas said: “Our new strategy obviously takes into consideration both the decision of the commission and the ongoing turmoil in the markets.”
He added that “the reorganisation of our network will allow us to address more effectively the challenges that surround us”.
A proposed merger between Olympic and Aegean was blocked in January on the grounds that it would have created a “quasi-monopoly” in the air transport market in Greece.