Up to 2,000 Irish jobs would be lost if duty-free shopping was abolished by the European Union, the SIPTU conference was told.
Air and sea fares would also rise sharply, leading to the withdrawal of some carriers and falling tourist numbers.
A delegate working at Shannon Airport, Ms Mary Cusack, said that an industry which had originated in a kiosk at Shannon airport in 1947, and which was now generating billions of pounds for the economy, was seriously at risk.
SIPTU president Mr Jimmy Somers told the conference it had already made its views known to the Minister for Public Enterprise, Ms O'Rourke, and would be meeting with the International Federation of Transport Workers to co-ordinate its campaign with the wider European trade union movement.