Ryanair is threatening to change its rules on cabin baggage, claiming some passengers have been causing delays.
The airline says its punctuality has suffered as a result of travellers abusing their allowance of a free second carry-on bag.
"We're seeing massive backpacks coming onboard, and with the best will in the world they won't fit in the overhead bins," says Ryanair's Chief Financial Officer, Neil Sorahan.
"This leads to delays at the gates. It leads to a number of bags having to be taken off before we take off, which can delay the departures. We're saying to our customers, please play by the rules."