Ryanair customers have expressed anger after the airline announced that passengers travelling with a young child will have to pay extra for a reserved seat.
Under the low-cost carrier's existing rules, all passengers can choose to save money by having their seats randomly allocated.
But the Dublin-based airline said this has led to "boarding issues" as crews try to re-seat adults and children who have been separated.
From September, one adult in every booking with children under 12 will have to purchase a reserved seat, which will cost half the standard £8 fee per flight.
Children under 12 will receive a reserved seat free of charge.
Other adults on the same booking will not be affected by the change.
A Twitter message posted by the airline which claimed it was making it "simpler and cheaper to fly with children" was met with frustration by a number of passengers.
Matt Ashby, from Blackpool, replied to the Ryanair post: "No, you're not as we now have to pay to reserve a seat, so will cost more."
A user named Pamela, from Ireland, wrote: "This is a joke right? It isn't cheaper. Just seat families together! No matter what age."
But some customers supported the measure.
Paul Connor described it as a "good move", adding: "Watching families give out when they can't sit together really bugs me - book the seats!"
Ryanair's chief marketing officer Kenny Jacobs said: "We are reducing the cost of a child's reserved seat to zero, and making it mandatory for one adult in each family booking to buy a reserved seat at the time of booking, which will cost just four euro (£3.37).
"This will make flying with Ryanair even cheaper and more simple for all customers with young children, and guarantee that they will always be seated together."