Immigration workers to join civil service pension strike Queues at border control at Heathrow airport. Hopes of an immediate respite for passengers facing lengthy passport queues at Heathrow and other British airports have been dashed after immigration border staff announced their intention to join next week's civil service strike over pensions. The Immigration Service Union, which includes most of the passport desk staff among its 4,500 members, said it was notifying the Cabinet Office that it intends to take part in the industrial action next Thursday. Ministers had announced an extra 80 "back-office" immigration staff were to be drafted in to work on the passport desks at the busiest times, after David Cameron and Theresa May agreed it was time to "get a grip" on the unacceptable queues at Heathrow. The move raised hopes that the worst of the passport crisis might be over. Lucy Moreton, the ISU deputy general secretary, said: "We don't want to cause disruption, but if the Cabinet Office continues to ignore our concerns over pensions then that is what we are going to do. We have hundreds of members at Heathrow so it will have a significant impact. In a recent ballot of ISU members, 73% of votes cast in a 32% turnout rejected the government's pension proposals. The package would replace retirement at 65 with a flexible retirement age, which the ISU claims could mean staff being forced to work until their late sixties. The immigration minister, Damian Green, said: "This strike is completely unnecessary and we believe the public will find it unacceptable if unions push ahead. The security of the UK border is of the utmost importance and we will use tried and tested contingency plans to ensure we minimise any disruption caused by planned industrial action. The former head of the UK Border Force, Brodie Clark, voiced concerns over a contingency plan to bring in a 600-strong "volunteer force" to staff border posts during the Olympics, when more than 660,000 extra visitors are expected. Clark warned that using volunteers from other parts of the UK Border Agency and Revenue and Customs could leave gaps in defending the border against smuggled drugs, weapons and other contraband. He also warned that plans to cancel border staff leave during the Olympics could result in severe difficulties in September and October, when there is a surge in overseas students at the start of the academic year.