London's Heathrow Airport has imposed a capacity cap of 100,000 daily departing passengers until 11 September.
It comes as one of Europe's busiest airports tries to control demand during the busy summer season amid a lack of resources.
No more than 100,000 daily passengers will be able to depart from today, the west London airport announced.
Airlines planned to operate flights with a daily capacity averaging 104,000 seats over that period, according to Heathrow.
The airport said it has ordered airlines to "stop selling summer tickets to limit the impact on passengers".
Heathrow chief executive John Holland-Kaye said: "Over the past few weeks, as departing passenger numbers have regularly exceeded 100,000 a day, we have started to see periods when service drops to a level that is not acceptable: long queue times, delays for passengers requiring assistance, bags not travelling with passengers or arriving late, low punctuality and last-minute cancellations.
"This is due to a combination of reduced arrivals punctuality (as a result of delays at other airports and in European airspace) and increased passenger numbers starting to exceed the combined capacity of airlines, airline ground handlers and the airport.
"Our colleagues are going above and beyond to get as many passengers away as possible, but we cannot put them at risk for their own safety and well-being."