It includes flights from Belfast to Edinburgh, Manchester and Birmingham as well as routes from Dublin to Manchester, Edinburgh and Glasgow.
British Airways (BA) CityFlyer will operate four routes from Belfast to Leeds Bradford, Exeter, Glasgow and Newquay for the rest of summer 2021.
Routes from Dublin to Kerry and Donegal and Belfast to East Midlands and Cardiff between now and at least 27 June have been cancelled.
The airline is "actively exploring" options that would enable the provision of a Dublin to Donegal service.
Customers impacted by the changes are being offered replacement or alternative flights.
