A tax of £13 on flights leaving Northern Ireland is giving the Republic of Ireland an advantage over the region, airport bosses have claimed.
The intervention came as Dublin Airport revealed it had a record 1.2 million passengers from Northern Ireland last year - a 37% increase on the previous 12 months.
The 1.2 million figure counts people leaving from and returning to the airport.
The airport said the "significant increase in passengers from Northern Ireland choosing to use Dublin Airport was due in part to a further expanded route network", including extra seats and new links.
Dublin Airport's chief communications officer, Paul O'Kane, added: "Passengers from Northern Ireland love the choice, convenience and value that Dublin Airport offers, with its extensive long-haul and short-haul route network and high-frequency connections to a huge number of destinations."
The airport also announced that more than two-thirds of all passengers visiting Northern Ireland who came by plane travelled through Dublin during the past year.
The number of people flying through Belfast City Airport to European destinations recently reached a record high, but its domestic routes have taken a hit.
And in the first eight months of this year, Belfast International Airport handled 3.38 million passengers.
A spokesman for Belfast City Airport said that while it had seen constant growth, the impact of air passenger duty (APD) was continuing to act as a drag on passenger numbers.
"Belfast City Airport has enjoyed sustained passenger growth in recent years, smashing our annual international passenger record in August this year and welcoming over 2.7 million passengers in 2015," he added.
"That figure will rise again in 2016, buoyed by the introduction of the successful daily KLM service to Amsterdam and the launch of our five times weekly service to Brussels.
The airport said there had also been increased frequency in its European summer services, which includes its Alicante route.
"We remain focused on bringing major new airlines and routes to Belfast City Airport," the spokesman added.
"Our accessible location also continues to prove a major attraction to passengers travelling to London and across the UK.
"That said, there's no denying that APD continues to put the region at a disadvantage to the Republic of Ireland, and we will continue to campaign for a resolution to APD that puts the local tourism industry on a level playing field with the rest of the island of Ireland."
This summer, it was revealed that Dublin Airport was the fastest growing major airport in Europe during the first six months of this year.
The data from ACI Europe, the trade association for European airports, showed passenger numbers at Dublin increased by 13.4% in the first half of the year.
That made it the leading performer among top tier European airports, which have more than 25 million passengers passing through them each year.
Last year, the airport saw record numbers, with 25 million passengers.
A third passenger terminal could be needed as soon as 2020, the Republic's Department of Transport believes. A department official also clarified that a review of the airport will not include an analysis of a new runway, which the department said will go ahead as planned.