Britain’s border control union said Wednesday it has set a strike date for May 10 as part of its dispute with the government over retirement ages. The strike by the union, which represents 4,500 border control officers who check passports and bags at customs, comes at a time of great tension at U.K. checkpoints. Long lines at London’s Heathrow Airport — some visitors have reported waits of more than two hours to have their passports checked — have become the subject of national concern with the country preparing to host the Olympics from July 27-Aug.12. Lucy Moreton, the deputy general secretary of the Immigration Service Union, said Wednesday that workers at major airports and seaports will be affected by the 24-hour strike. Border controls in Paris and Brussels connected to the Eurostar train service will also be affected. “It is with deep regret,” Moreton said of the strike. The union is demanding its employees be exempt from government increases in the retirement age because of the physical nature of their jobs. Britain’s immigration minister Damian Green called the strike unnecessary. He said the “public will find it unacceptable” if the strike goes forward. “The security of the U.K. border is of the utmost importance and we will use tried and tested contingency plans to ensure we minimize any disruption caused by planned union action,” he said. Green earlier this week acknowledged that “there is a problem” with long waits at airport immigration lines and said Britain’s border force would deploy extra staff at Heathrow amid growing furor over the slow-moving lines. The U.K. Border Agency would not comment on the “tried and tested” contingency plans that Green was referring to or how much disruption the strike was expected to cause. In November, contingency plans for a strike saw extra hands — including civil servants such as Prime Minister David Cameron’s policy unit and his press secretary — drafted in to help staff immigration desks and minimize disruption.