Airlines face accusations of holding onto millions of pounds of refunds which should have been issued to passengers.
People who fail to take a flight they have booked should be able to reclaim the tax proportion back.
But consumer watchdog Which? has said most carriers make it too difficult to get the money returned.
Passengers should be able to reclaim Air Passenger Duty which varies from £11 per person on a flight within Europe, to £110 for a long-haul first class flight.
Most airlines charge passengers an administration fee if they want to reclaim the tax.
The fees range from Ryanair’s charge of £17 per person, Flybe at £25 and British Airways and Virgin Atlantic of up to £30.
Only Easyjet is among major carriers will refund the tax for free.
Which? spokeswoman Rochelle Turner said: “In some cases it costs at least twice as much to reclaim the tax as the tax itself.”