Holidaymakers in Spain this summer are facing a surprise new airport tax imposed by the Spanish government as it tries to balance its books.
Some airlines are passing the new departure tax on to passengers, even if they booked their flights months ago.
Some passengers have received emails telling them either to pay an extra charge of up to seven euros (£6) per person - or to cancel their flights.
Other airlines are deciding whether to absorb the cost themselves.
The budget airline Ryanair said Spain's 2012 budget, passed into law at the end of June, obliged airlines to pay increased taxes.
Spain is implementing drastic measures to try to slash its budget deficit to 5.3% from 8.5% in 2011.
It has been promised bailout funds of up to 100bn euros for its banks, but wants to avoid a full state bailout.
The European travel agents' association ECTAA said the amount of the extra levy varied depending on which airport people used.
It said the average rise in the tax was 18.9%, but at some of the larger airports it would almost double.
For instance, at Madrid-Barajas the tax would rise from 6.95 euros to 14.44, while at Barcelona's El Prat airport it would rise from 6.12 euros to 13.44.
Ryanair said it would pass the cost on to passengers, even those who had already paid in full for their flights, because the tax applied "retrospectively to customers who booked flights before 2 July 2012 and are travelling from 1 July onwards".
It said for bookings made on or after 2 July, the increased tax would have been included in the price.
The Spanish low-cost airline Vueling is also passing on the cost. It sent emails to passengers giving them seven days to cancel their flight, or the extra payment would be debited automatically from the card they used to book.
British Airways and Iberia told the BBC they had not yet decided whether to pass on the cost or absorb it.
ECTAA said in a statement it was "dismayed" by the rise, which was imposed "without proper consultation of airport users nor appropriate implementation time".
It said travel agents faced a "technical and financial nightmare to recover the extra charge".