Two airlines have confirmed they are cutting a number of routes from Belfast.
Aer Lingus will cut flights from Belfast City Airport to Faro and Malaga after a commercial review found the routes were not performing in line with expectations.
Ryanair said it is dropping a number of loss-making routes but a spokesman for the airline did not confirm which ones will be cut.
"As announced on July 16, due to the late delivery of up to 30 Boeing MAX aircraft, a number of loss-making Ryanair bases will be cut or closed this winter," he said.
"We are working hard to minimise the impact on our customers and our people, and to continue as many routes as possible, which will be served by flights from other bases."
A spokesman for Belfast International Airport (BIA) blamed Air Passenger Duty (APD) for the cuts, claiming it disadvantages airlines operating from the region.
APD does not apply on long haul flights from Northern Ireland and airports have lobbied for it to abolished on short haul journeys.
The spokesman said: "Naturally, We are extremely disappointed at this further reduction in service.
"The airport has worked hard with Ryanair over the last four years to build, develop and sustain these direct routes.
"Yet again this highlights the taxation disadvantage posed by Air Passenger Duty (APD) on airlines operating from Northern Ireland.
"We have consistently highlighted the problem which Air Passenger Duty (APD) in Northern Ireland creates for air service development and job creation.
"Our hope now is that with this news, the Government will see the damage that APD continues to do to our sector and the impediment the tax creates to attracting and maintaining services."
He added, "By failing to remove the competitive barrier that is APD, the Government is denying Northern Ireland passengers destination choice and an air travel sector that offers considerable potential.
"There remains a strong market demand for direct air services to those destinations which will no longer be served by Ryanair.
"We have already secured some additional capacity to the Canary Islands and will continue to work with our airline partners to replace lost services."
A spokeswoman for Aer Lingus said, "In 2020, Aer Lingus will continue to deliver a high frequency daily service between Belfast City and London Heathrow.
"In summer 2019, Aer Lingus increased frequencies on the route to four times daily on Tuesdays, Wednesdays, Thursdays and Saturdays."