The European Consumer Centre in Dublin has said it has received more than 4,000 complaints a month since March over cancelled flights.
The majority of the coronavirus-related complaints relate to refunds on bookings made earlier in the year.
Diana Valentine, from ECC Ireland, said sea and land trips are also causing immense concern among consumers.
Ms Valentine said: "Over 2020 to date, we have dealt collectively with over 25,000 coronavirus-related complaints out of which 22,700 were in connection with cancelled flights.
"This was followed by sea and land journeys."