A Which? Travel investigation found surcharges were commonplace for phone bookings, with firms looking to direct business online.
According to Which?, Ryanair and Tui charge an additional £20 when booking by phone, easyJet £15 and British Airways £10.
Jet2.com was the only airline investigated by Which? that did not apply a phone bookings surcharge.
Rory Boland, editor Which? Travel editor, said: “Not all customers are comfortable booking online, and they should not be penalised for booking over the phone.
“Airlines that are charging customers more must be clear and transparent about these additional fees.”
Which? approached Ryanair, Tui, easyJet and BA for comment.
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 passengers requiring special assistance can access cheaper online prices by phone.
Ryanair said less than 0.5% of its customers choose to book by phone, while BA and Tui said phone bookings incurred an admin cost.
