British Airways, Easyjet and Ryanair are warning British holidaymakers of delays at EU border controls.
BA has sent text alerts asking travellers to arrive early, as it expects longer queues due to "enhanced immigration checks" across Europe.
The airline has already sent texts to customers flying back from Lyon, Madrid, Barcelona and Milan.
Ryanair is also advising customers to arrive at least three hours before their departure time.
Easyjet is urging people to check its website for updates and allow plenty of time to get through the airport.
The airline has also warned of strike action due at Barcelona airport every Friday, Sunday and Monday from 4 August throughout the summer.
A spokesman for Airlines for Europe (A4E), the airline lobby group, told the BBC: "It seems the governments - especially in France, Italy, Spain, Portugal and Belgium - underestimated the situation of many passengers going through tighter passport checks and have not provided a sufficient amount of border control officers."
He said passengers should expect delays at airports in Majorca, Malaga, Lisbon, Lyon, Brussels, Milan and Paris Orly.
'Abusive' security staff
Passenger Kate Meeks says she was one of 22 people who missed her flight from Barcelona to Birmingham.
She had arrived three hours early at Barcelona Airport, where there is also strike action among security staff, but was only told about the extra passport control half an hour before take-off.
"Little did we know we had to go through an extra passport control where there were 1,000 people trying to get four flights at the same time," she told the BBC's Victoria Derbyshire programme.
Ms Meeks said two men due to take the Birmingham flight tried to get to the front of the queue, but were told to join the back or be removed from the airport.
"It was absolutely horrendous," she said. "Twenty-two of us begged to go on the plane, and they said that they couldn't let us on... But it took them half an hour to get our luggage off."
She said she spent £500 on booking a hotel room for the night and missing a day's work, adding that staff at passport control were "rude and very abusive".
"This has caused an absolute nightmare for all of us through missed flight connections, financial cost, mental cost," she said.
The warning comes as airports prepare for one of the busiest weekends of the summer.
Sean Tipton, from the Association of British Travel Agents, said a record 2.4 million people had already set off in one weekend at the beginning of the school holidays.
He said: "In most cases people are getting through passport control fairly swiftly, but I think there might be an issue with certain airports where they haven't actually considered just dealing with the fact that: record numbers, August, plus these new requirements - they may be understaffed."
A spokesman for Ryanair also blamed the delays on European border control authorities, claiming that the airline's operations are "running as normal".
He said the delays are a matter for the European regulators to resolve, not the airlines.
Easyjet advised passengers to check the latest travel information pages on its website, adding that it "strongly recommends" customers to allow extra time to get through the airport to the gate on time.
The UK's aviation minister, Lord Callanan, has said he will urge his counterparts in Portugal, Spain and Italy to "do all they can to reduce queues and allow travellers to get on with their holidays".
Thomas Reynaert, managing director of A4E, told the BBC that the French and Spanish governments have promised extra staff, but so far "we haven't seen any concrete improvement".
The European Commission said the delays were "the price of security".
Rule changes brought in after recent terror attacks in Paris and Brussels mean people entering and leaving the Schengen area, which allows passport-free movement across much of the EU, face more security checks.
Under the new measures, 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.
But A4E said that some passengers are facing delays of up to four hours, claiming that some European airports are producing "shameful pictures of devastated passengers in front of immigration booths".
Mr Reynaert said member states "must take responsibility for this".
He warned the regulations have not yet been fully implemented across all member states, which "may lead to even more disruption during the next few weeks".
The member states have until 7 October to put the new rules in place.
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