Four of the five biggest UK airlines charge extra for book by phone, according to Which? Travel.
Ryanair and Tui both add a £20 surcharge for flights that are not booked through their websites. EasyJet charges £15 and British Airways £10.
Only Jet2.com told the consumer group that it will not charge extra for booking by phone.
Other airlines claim phone bookings add an admin cost. Ryanair said that more than 99.5% of its customers book online.
However, Ryanair carried 129 million passengers in 2017, meaning that it could have made around £6 million in surcharges from passengers who can’t or won’t use the internet, assuming there were two people per booking.
Ryanair told Which?: “It has never been easier to book a flight at Ryanair.com or on our Ryanair App and less than 0.5% of our customers choose to book over the phone or at the airport.
“A €20/£20 fee applies to reservations made at airports or call centres in order to offset the associated administration costs.”
EasyJet said: “We encourage passengers to book online. Those using our telephone service are informed of the online discount at the beginning of the call.”
The airline added that those passengers requiring special assistance do not have to pay the £15 charge. Instead, they should use a dedicated customer support telephone service.
“Fees for booking by phone are just one of a number of extra charges that push airfares up, including check-in fees, allocated seating and hold luggage,” Which? said.
“We recently reported that add-on prices can make ‘no-frills’ more expensive than paying for a traditional full-service flight.”