Travellers will be charged a £6 administration fee unless they use a Ryanair Cash Passport card to book flights.
The move has been criticised by consumer groups who say that customers are growing tired of paying for extras not included in the original price.
A spokesman for Scotland's consumer watchdog, Consumer Focus Scotland, said: "Consumers shouldn't have to sign up to special cards to avoid paying excessive fees.
"People want the price advertised to be the price they pay. They don't want to be confused by finding a cheap headline price only to discover hidden costs when they delve beneath the surface.
Ryanair's Stephen McNamara said: "Only Ryanair delivers the lowest airfares and no fuel surcharges guaranteed."
Ryanair has a bewildering array of extra charges which some commentators have suggested amount to hidden costs.
Passengers who want to change the name on their flight booking can be charged up to £160.
Just putting one bag in the hold during peak times incurs a cost of up to £55. The cost of stowing a second bag can cost as much as £85.
The airline's "infant fee", which needs to be paid when carrying a small child, is £20.
Last summer, the no-frills airline announced it would charge customers £1 to use the toilet.
The airline wanted to encourage passengers to use toilets before or after the flight, in the hope of eventually ripping toilets out of all of their planes and cramming in a few more seats.
Prices differ wildly depending on whether you make a booking via the Ryanair website or by directly speaking to Ryanair staff at a call centre or airport desk.