A nationwide public-sector strike next Wednesday in Britain threatens to paralyze operations at Heathrow, Europe's busiest airport.
BAA, the airport's operator, said Friday 12-hour delays for arriving passengers are likely because the Nov. 30 strike will hit the U.K. Border Agency's ability to support normal operations.
An estimated 2 million workers are expected to protest changes in public-sector pensions with a 24-hour walkout _ billed as potentially the biggest union action since 1979.
The lines at Heathrow's immigration counters are expected to be so long that passengers will need to be held on planes, BAA warned.
"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 U.K. for arriving aircraft," Normand Boivin, the chief operating officer for Heathrow, warned in a letter to airlines.
The letter, written Thursday and shared with The Associated Press, urged airlines to reduce the number of passengers they bring in on Nov. 30 because BAA had "reluctantly concluded that the U.K. Border Agency wouldn't be able to come up with a contingency plan to ensure business-as-usual."
Boivin said the border agency expects to be functioning at less than 50 percent of normal productivity.
British Airways and Virgin Atlantic Airways both agreed to waive fees for rebooking flights on Nov. 30 and expressed concern over the strike's impact on business.
The U.K. Border Agency acknowledged travelers could see longer waiting times at airports but said it has considered "all options" to make sure it's prepared for the strike and aims to minimize any disruptions.
It said the security of Britain's borders is the agency's top priority, though unions have criticized moves to draft in civil servants and contractors to cover for striking immigration officials.
"Our members take two to three months to train - the idea that people can cover after a few days' training is absurd," said Mark Serwotka, leader of the Public and Commercial Services union.
The Home Office said it has undertaken "significant work" to plan for the strike, which includes training managers, staff and contractors to the high standards it requires to carry out border checks and asking staff around the world to provide additional cover on Nov. 30.
Government ministers have warned the nationwide could cost the economy half a billion pounds and lead to job losses.
Heathrow Airport handles 180,000 passengers on a typical day, according to BAA.
Gatwick Airport also warned passengers to be prepared for "significant disruption" at immigration and said it asked carriers to give passengers the chance to change their flights.
Gatwick's chief operating officer, Scott Stanley said the airport is working with the border agency and airlines to put contingency measures in place and ensure disruptions are kept to a minimum.
"Unfortunately, airport staff cannot man the desks at the border zone but we will provide all necessary assistance to the Border Agency and we are determined to make sure that the needs and welfare of all our passengers will be met on the day," Stanley said.
Cassandra Vinograd can be reached at http://twitter.com/CassVinograd