Large scale Ryanair expansion in Northern Ireland is prohibited by the cost of air passenger duty (APD), a spokeswoman for the company said.
Airlines have led efforts to scrap the tax which they believe is distorting competition. Concessions have already been granted reducing charges on direct long haul routes after United Airlines threatened to pull out from the Belfast to Newark route.
Airlines are paying £26 per passenger for a domestic return flight.
Kate Sherry, deputy director of route development at Ryanair, told the Northern Ireland Affairs Committee of MPs: "APD prohibits large scale expansion into Northern Ireland to the detriment of industry and tourism connections. However, we continue our dialogue with the airports."
She added there was a difference between large scale expansion, the sort that would deliver real value to the economy, and talks which the company is engaged in with Northern Ireland airports.
"We are in discussions with over 200 airports. We have a large presence, the third largest airline in the UK despite APD," she added.
Ryanair flies from the City of Derry, but left George Best Belfast City Airport in 2010, citing delays in building a longer runway.
Paul Simmons, UK director at easyJet, said APD acted as a brake on people travelling and said it was a major proportion of the ticket cost.
"This is an unfair tax overall, but it's especially unfair for the people of Northern Ireland. And if this tax is increased, it will have a serious impact on tourism," he added.