Ryanair is tightening the rules on what passengers pay to take luggage onto the plane, in order to "speed up boarding".
From November, passengers will still be allowed to take one "small personal bag" into the cabin, as long as it will fit under the seat in front.
But they will have to pay £6 if they also want to take a 10kg bag, such as a pull-along suitcase, on board.
And they'll still have to pay up to £10 if they want to check that bag into the hold instead.
The move is not aimed at making money, the airline said, but was intended to "improve punctuality and reduce boarding gate delays".
Under the new policy only 95 passengers per flight - around half of the total - will be permitted to pay for the right to take the extra bag on board.
Other travellers will have to pay £8 to £10 for their 10kg bag to go into the hold. Larger checked-in luggage will still cost £25 per bag.
It is the second time in a year that Ryanair has altered its cabin luggage policy.
Rival airlines such as Easyjet, Wizz and Norwegian allow one piece of free hand luggage in the cabin on short-haul flights.
Ryanair said it was increasing the size of the small carry on bag that remains free to take on board to 20 litres.
Kenny Jacobs, Ryanair's chief marketing officer, said the new policy "will speed up boarding and cut flight delays" by encouraging people to either travel very light with just one small bag, or to check-in a medium-sized bag.
Currently Ryanair allows customers a small personal bag, and passengers who have paid for priority boarding can take a 10kg bag into the cabin as well.
Those without priority boarding currently take pull-along bags and other medium-sized luggage with them until they board at the gate - at which point bags are transferred to the hold free of charge, which means passengers can take two bags without paying extra fees.
But Ryanair said this policy was causing delays.
From November, if passengers turn up at the boarding gate with more than the 20 litre carry-on bag but haven't paid for the priority boarding status, the bag will be placed in the hold at a charge of £25, Ryanair said.