More strikes have been announced by Border Force staff at Heathrow Airport at the back end of half term.
The strike action will take place on 31 May and 1 and 2 June.
It will be followed by three weeks of action short of a strike, including staff working to rule and a ban on overtime running from 4 until 25 June.
More than 500 members of the PCS (public and commercial services) union will take part in the strikes, which come following a dispute over a new staff roster.
The PCS said it expects the walkouts to disrupt passport checks for travellers coming into the UK at the airport.
The staff, who work in terminals 2, 3, 4 and 5, held four days of strike action last month.
The union said it had written to the Home Office following the previous industrial action “highlighting the many problems raised” with the new system.
Its general secretary Fran Heathcote said: “We are keen to resolve this dispute but the Home Office must first put something on the table for our members to consider.
“The Home Office has said it is ‘open to discuss’ a resolution but it only responded to our request for a meeting after we threatened further action.
“Until it comes back with changes to the roster that will benefit our members then the dispute will continue.”
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A spokeswoman for Heathrow Airport said it would be working with the Home Office on contingency plans to minimise disruption to passengers.
She told Sky News that past strikes had been “dealt with well” and “managed successfully”.
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A Home Office spokeswoman said: “We are disappointed with the union’s decision to strike but remain open to discussing a resolution with PCS Union.
“The changes we are implementing will bring the working arrangements for Border Force Heathrow staff in line with the way staff work at all other major ports, provide them with more certainty on working patterns, and improve the service to the travelling public.
“We have robust plans in place to minimise disruption where possible, but we urge passengers to check the latest advice from operators before they travel.”
