Heathrow Airport bosses have warned that passengers could face delays of up to 12 hours next Wednesday, as immigration offers join the public sector strike.
The strike, to be held on Wednesday, 30 November, will see up to 2.6 million public sector staff walk out in a dispute over pension changes.
The Immigration Service Union has 4,000 members, most of whom are expected to take part in the 24-hour walk out.
Heathrow operator BAA has been in discussion with airlines and the UK Border Agency to try and minimise the impact of the strike on members of the public.
Members of border staff who are not union members will be asked to carry out airport immigration checks, as will Whitehall civil servants.
Airport managers are also expected to step in to help with the back-log of immigration checks. And in an effort to reduce delays, carriers are being asked to fly planes at half capacity.
“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,” Norman Bolvin, Heathrow’s chief operating officer, told the Daily Telegraph.
“This in turn would quickly create gridlock at the airport with no available aircraft parking stands, mass cancellations or departing aircraft and diversions outside the UK for arriving aircraft.”
The Treasury has said that the strikes could cost the UK around £500 million and even lead to job losses. But Brendan Barber, general secretary of the Trades Union Congress has called this figure “fantasy economics”.
Mr Bolvin added: “Modelling of the impacts of strike action on passenger flows at Heathrow show that there are likely to be very long delays of up to 12 hours to arriving passengers.”