Ryanair has said many customers will no longer be able to take two pieces of luggage into the cabin.
The budget airline said passengers without priority boarding would have to put their second bag in the hold free of charge at the gate.
For bigger bags Ryanair is cutting fees from £35 to £25 to encourage customers to check in more luggage.
Ryanair said it was making the changes from November to ease delays after too many customers took two bags on board.
The airline said earlier this year it was a “victim” of its own “niceness” after allowing customers to bring a second carry-on bag for free.
It said “abuse” of that policy was contributing to flight delays, with people taking on bags up to three times the permissible size.
Under the changes announced on Wednesday, Ryanair passengers without priority boarding will only be able to take one smaller carry-on bag on board the aircraft.
At the same time it is lowering checked-bag fees and increasing the check-in bag allowance from 15kg to 20kg.
Ryanair’s chief marketing officer, Kenny Jacobs, said: “These bag policy changes will cost Ryanair over €50m (£46m) per annum in reduced checked bag fees.
“However, we believe offering bigger bags at reduced fees will encourage more customers to consider checking-in a bag, which will reduce the high volume of customers we have with two carry-on bags at the boarding gates.”