Heathrow Airport announced it has introduced a cap of 100,000 daily departing passengers until 11 September as Britain's aviation industry struggles to cope with the post-pandemic demand for travel.
Airlines had planned to operate flights with a daily capacity averaging 104,000 seats over that period, the West London airport said on Tuesday.
Britain's busiest airport said daily departing seats are set to be 4,000 over its new 100,000 cap, and on average 1,500 of these seats have already been sold to passengers.
As a result, it has told airlines to stop selling summer tickets to "limit the impact on passengers" as it grapples with long queues, flight delays and cancellations due to staff shortages and strikes.
The airport also grounded 61 out of around 1,100 scheduled flights on Monday, affecting around 10,000 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 wellbeing."
Carriers have also been slashing their flight schedules as pressure mounts.
Low cost European carrier Wizz Air (WIZZ.L) said will slash its peak summer flight programme due to the chaos at airports, trimming its capacity by another 5%.
Europe’s biggest airline Lufthansa (LHA.DE) plans to cut domestic and European flights from Frankfurt airport between Friday 8 July and Thursday 14 July to provide a stable flight plan.
Last week, Scandinavian airline SAS (SAS.ST) cancelled nearly 70% of its flights as a pilot strike stranded thousands of tourists overseas.
It comes after the UK government recently created an "airline slot amnesty", giving carriers permission to cancel flights without incurring fines in a bid to minimise the aviation mayhem.