Flybe has cancelled three of its Belfast City Airport flights and decreased the frequency of five other routes during summer.
Due to late aircraft deliveries, flights will not be able to fly to Newcastle, Inverness, and Aberdeen.
Operators will be able to offer reduced services to Birmingham and Edinburgh, Glasgow, Manchester, Southampton, and Manchester.
Dave Pflieger (the airline's chief executive) said that the decision was not taken lightly.
The airline has decided to cancel a planned increase in flights from 28 July to 29 Oct., after stating that two aircraft leasing companies were not able to fulfill their obligations until the end of the summer.
The airline has rented aircraft from 2 different airlines, one in Greece and one Spain. However, the additional aeroplanes are not sufficient to meet the increased schedule.
It also promised that it would add more flights in the coming year.
"This is not an easy decision, and we are having daily conversations with all parties to see if there might be any changes that would allow us resume our original plans at a later date." said Mr Pflieger.
"It is crucial that we act now to ensure that you have sufficient time to make changes to your travel plans, be re-accommodated with a different flight, or, if it is not desired, receive a full refund."
He said: "I would like to apologize again to anyone affected by this announcement; I thank everyone who flew on us to this point; and we renew our commitment to doing everything possible to improve our company and keep our customers informed as our business grows and serves you and your communities."
According to the airline, customers can request a refund or change their flight via their website.
