The UK summer holiday getaway is just about to start
Varied policies exist among airlines on booking charges when customers use credit or debit cards, according to the consumer association Which?.
Some charges have risen in the last 18 months while another airline has stopped levies on passengers who pay for bookings with plastic cards.
Charges applied should reflect costs to the airlines, Which? said.
Millions of families will fly across the EU in the coming weeks, as UK schools close for the summer.
Which? Holiday magazine found that - based on flight tickets for two adults costing a total of £300 - Thomas Cook UK charged £10 per booking for using a debit card and First Choice customers paid £2.50. Eighteen months ago neither levied a charge.
A spokesman from Thomas Cook said several types of credit and debit cards could be used to purchase flights and some did not attract a fee.
Ryanair has increased fees from 70p to £5 per person each way for debit cards bookings - except for Visa Electron which is free - and from £2 to £5 for credit cards, in the last 18 months.
The airline said it expected 20 million Ryanair passengers to use Electron cards in 2009.
Wizz raised charges to book using a debit card from 70p per person each way to £4.
But the magazine found that while Bmibaby levied a 1% charge for paying with a debit card 18 months ago, there was now no charge.
Virgin Atlantic had changed its policy to charge 1.3% per cent of the total booking for credit card payments, instead of £3 per person, which was cheaper for the sample used by the magazine. BA did not charge for using a debit card to pay for flights.
"We understand that there is a charge to airlines for taking payment for flights with debit or credit cards and that this cost will be passed on to consumers," said Lorna Cowan, editor or Which? Holiday.
"The amount charged by the airlines should be reflective of the costs incurred by them. This does not appear to be the case with current charges, and we are concerned that airlines may be using them as a way of boosting profits."
Michelle Whiteman, of the UK card association, said that charges should be made clear upfront to customers.