Aer Lingus will terminate its Belfast City-London Gatwick service next year.
The airline will cease its thrice-daily operation between the two cities on March 27.
Ryanair is reportedly bidding for the newly-vacant LGW slots, with any service likely to be operated from Belfast International airport.
A spokesman for Aer Lingus said: "Customers who had existing bookings on the route will be offered three alternative options - flights from Belfast City to London Heathrow, flights from Dublin Airport to London Gatwick or a full refund. Aer Lingus will communicate directly with customers about this schedule change in the coming days.
"While the Belfast City to Gatwick service will be discontinued Aer Lingus continues to operate a high frequency service between Belfast City and London Heathrow.
"Flights between Belfast City Airport and London Heathrow will benefit from a 21 per cent capacity increase due to the deployment of a larger A320 aircraft adding 35,000 extra seats over the 2016 summer schedule."
Aer Lingus became part of IAG in the summer (see news, August 19).