Heathrow airport operator BAA has asked airlines to halve the number of international passengers arriving into the UK on 30 November, when border staff strike over pensions.
BAA, owned by Spanish infrastructure group Ferrovial, on Friday warned of significant disruption to passengers arriving at Heathrow next Wednesday with delays that could last up to 12 hours.
"We will plan for a normal flight schedule, but we are requesting all carriers to reduce load factors on each international flight arriving into Heathrow on November 30 to 50 percent of normal levels," Normand Boivin, Heathrow's chief operating officer said in a letter sent to Heathrow's largest airlines.
"The delays at immigration are likely to be so long that passengers could not be safely accommodated within the terminals and would need to be held on arriving aircraft. This in turn would quickly create gridlock at the airport with no available aircraft parking stands, mass cancellations of departing aircraft and diversions outside the UK for arriving aircraft."
IAG-owned British Airways, Heathrow's largest carrier, and Virgin Atlantic are offering alternative dates to passengers due to travel on 30 November.
London's second largest airport, Gatwick, has also asked airlines to rebook passengers.
"The UK Border Agency (UKBA) currently expects to perform at less than 50 percent productivity. We have reluctantly concluded that UKBA will be unable to provide a contingency plan to support normal operations," added Boivin.