UK holidaymakers flying home from Europe this weekend are being urged to arrive at airports at least three hours before their flight because of chaos caused by new passport controls.
Queues of up to four hours have been reported since the introduction of more stringent checks on travellers entering and leaving the Schengen area, which allows passport-free movement across much of the EU.
Airports in Spain, Portugal, France, Italy and Belgium have been affected.
The situation could worsen this weekend as lobby group Airlines For Europe (A4E) warned it will be one of the busiest of the year with 10 million people expected to pass through European airports on Saturday and Sunday combined.
Some airports, such as Majorca, are predicted to experience double their usual demand.
British Airways, easyJet and Ryanair have all alerted passengers to the need to turn up at airports earlier than normal.
Ryanair issued an alert which urged its customers to arrive "at least three hours before the scheduled departure time".
BA is sending text messages to passengers flying back from airports where long lines at border controls are expected.
A spokeswoman said: "We're texting customers flying from airports that we know are having issues to ask them to arrive early."
The carrier has promised that any customers who miss their flight because of the queues will be re-booked for free.
The extra security measures were brought in following terror attacks in Paris and Brussels.
They have led to long lines at border controls as the details of passengers from non-Schengen countries - such as the UK - are run through databases to alert authorities if they are known to pose a threat.
Ryanair boss Michael O'Leary said earlier this week that more than a fifth of the airline's flights were being delayed because of the issue and he is "jumping up and down" in frustration.
Just 78% of the Dublin-based carrier's flights were on time on Tuesday, down from 90% during the month of August as a whole last year.
Aviation minister Lord Callanan has been in touch with other governments over the issue.
"I hope it's teething problems," he said. "We are certainly in contact with other governments across Europe to do all we can to mitigate them and to make it easier for people who are trying to enjoy their hard-earned break abroad."
European Commission spokeswoman Mina Andreeva said there was a "price to be paid" for security, but insisted that EU countries should have put arrangements in place to avoid lengthy queues.
At a press briefing in Brussels, she said: "We understand there are concerns about EU rules that might lead to longer waiting periods. But this is very clearly about the security of our citizens and it is member states that have called for these rules, unanimously, in the European Council in October 2015."
She added: "There is always a price to be paid for security and also member states had enough time to prepare for the entry into force of these rules.