Border Force staff at Heathrow Airport have voted to strike in a dispute over shift patterns.
The Public and Commercial Services Union (PCS) said 600 of its members, who carry out immigration controls and passport checks, voted 90% in favour of industrial action.
No dates have been announced for any strike action, but walkouts could begin as soon as 8 April, the union said.
A Home Office spokesperson said they had "robust plans" to minimise delays.
The union said its members are angry at planned alterations to their shift patterns that would have a detrimental effect on them and leave nearly 250 without jobs on passport control.
If they refuse to accept the new contracts they would be forced to seek jobs elsewhere in the Home Office, the PCS said.
'Unnecessary changes'
Union general secretary Fran Heathcote said: "It's clear from today's ballot result how angry and determined our members are to protect their jobs.
"It's not too late for the Home Office to do the decent thing and drop these unnecessary changes and work with the union to protect jobs and working conditions.
"PCS is currently challenging the government's minimum service levels legislation in the courts.
"We will vigorously defend our members' right to strike if ministers try to impose a work notice."
A Home Office spokesperson said: "As the public would expect, our priority is to keep our citizens safe and our borders secure.
"We are working closely with Heathrow Airport and have robust plans in place to minimise any delays from planned strike action.
"We will deploy suitable resources to meet critical demand and support the flow of passengers and goods through our border."
Listen to the best of BBC Radio London on Sounds and follow BBC London on Facebook, X and Instagram. Send your story ideas to hello.bbclondon@bbc.co.uk
Source: https://www.bbc.co.uk/news/uk-england-london-68642474