Military personnel, civil servants and volunteers from across the government are being trained to support Border Force as strikes loom at airports and ports across the UK.
Members of the Public and Commercial Services (PCS) union working at Gatwick, Heathrow, Manchester, Birmingham, Glasgow and Cardiff airports are due to strike for eight days between December 23 and 31 in a dispute over pay.
A government statement said Border Force is ready to deploy resources “to meet critical demand” but warned “those entering the UK should be prepared for potential disruption”.
It added: “Border Force and the travel industry work together very closely at a local and national level to agree plans for pressures while keeping the public safe.
“Those who are due to travel into the UK during the proposed industrial action should be prepared to face longer wait times at UK border control.
“All passengers should check the latest advice from their operators before travelling.”
The statement also urged all passengers to use eGates if they can.
The industrial action was announced last week by Mark Serwotka, general secretary of the Public and Commercial Services (PCS) union, which represents civil and public servants, and private sector workers on government contracts.
He told BBC Radio Wales Sunday Supplement: “It would be completely wrong for anyone to think that the way to solve an industrial dispute is to ask our armed forces to effectively come in and strike break.”
Heathrow has pledged that the “vast majority” of arriving passengers should be unaffected by Border Force strikes in the lead-up to Christmas.
“We are doing everything we can to protect a full flight schedule on strike days, so departing passengers should expect to travel as normal,” it said on Monday morning (December 12).
More: ‘Vast majority’ of passengers to be unaffected by Border Force strikes, Heathrow pledges