Ryanair boss Michael O'Leary will appear before the Oireachtas Transport Committee later.
He is set to outline the effect the €10 travel tax is having on the airline and tourism industries.
Mr O'Leary says the tax will end up costing 3,000 jobs, €480m in lost revenue and will lead to 1.2 million fewer departing passengers.
Chairman of the Oireachtas Finance Committee, Fianna Fáil TD Frank Fahy, says the tax is needed to get the state's finances back into shape.