Dozens of Ryanair passengers were left stranded in scorching 30C heat in Greece after their flight to the UK left without them.
Between 20 and 50 passengers missed Sunday's flight from Athens International Airport to London Luton, according to the BBC.
The incident is the latest to fuel concerns over delays linked to the EU's new Entry/Exit System (EES), which was introduced to tighten border security across Europe.
Ryanair blamed border delays for the disruption, while Athens International Airport pointed to congestion caused by "additional processing requirements", though neither directly said the EES was responsible.
Since it was implemented, EES has faced a number of operational hurdles, which has led to the EU border agency Frontex to warn that the system may take up to two years to fully stabilise.
The Mirror's travel writer Milo Boyd, who managed to board Sunday's flight to Luton, said there was a "mega queue" at both security and passport control.
He said tensions boiled over, recalling how one passenger shouted: "You can't do this. It's ridiculous!"
Boyd and his wife made it to the gate with just 10 minutes to spare, but he estimated that at least 20 passengers arrived too late and were left behind.
"These poor people were pleading with the Ryanair staff to let them through - one guy was crying, another guy looked like he was about to explode," Boyd told the BBC.
Authorities reportedly stepped in to maintain order.
A spokesperson for the airport told the BBC there had been "periods of congestion at passport control in the departures area due to high passenger volumes and the additional processing requirements associated with travel to non-Schengen destinations".
They added: "As is currently the case at many European airports, passenger flows on certain routes may experience increased processing times as new border-control procedures continue to be implemented and refined."
Ian Collins said in an X post to Ryanair that it was "utterly disgraceful you left my daughter (and half your passengers) at the gate in Athens today".
Ryanair said in a statement that "a number of passengers" did not board in time "due to delays caused by border control at Athens airport".
It added: "All passengers that were at the boarding gate when this flight from Athens to London Luton boarded, travelled without incident."
