Ryanair and Wizzair have been fined €3m and €1m respectively by Italy's Competition Authority (ICA) over their cabin bag policies.
Both budget airlines have a policy whereby small cabin bags can only be placed in the cabin free of charge if they can be stowed under the seat in front of the passenger.
Any bigger bags weighing up to 10kg cost extra, for example upgrading one's plane ticket to a priority boarding pass.
The ICA said that requiring customers to pay between €5-25 extra in order to bring cabin bags aboard was misleading and a "non-transparent" way to raise ticket prices.
Ryanair has hit out against the decision, according to AFP, saying its policy was transparent and helped flight punctuality as it speeded up boarding.