Immigration staff are to stage a one-day strike in the bitter dispute over public sector pensions, threatening huge disruption at airports including Heathrow, which is already being hit by massive delays.

The Immigration Services Union (ISU), which represents 4,500 Border Agency staff, said its members will walk out next Thursday, May 10, at ports and airports across the UK and abroad.

The union said it was in dispute with the Government over plans to increase the retirement age for public servants, linking it to the state retirement age.

The Government is already dealing with complaints about long queues at Heathrow and is planning to draft in 80 extra staff.

The ISU said it believed managers would be used to cover for its members during next week's strike, which is being held on the day tens of thousands of civil servants, lecturers, health staff, Ministry of Defence employees and members of the Royal Fleet Auxiliary also take industrial action.

"The Government will run some kind of skeleton service. If the airlines advise people not to travel on that day things might be quiet," said a union spokesman. "We want a fixed retirement age of 65 for immigration staff."

Immigration minister Damian Green has admitted the Border Force needs to change the way it operates and said the extra staff would start work this month.

But Mark Serwotka, general secretary of the Public and Commercial Services (PCS) union, warned: "Drafting in staff from other areas of an already overstretched agency is like putting a sticking plaster on a serious injury, it will do nothing to stop the inevitable from happening."

Labour said some 1,500 Border Force staff were being cut as the management of Britain's borders drifted "from one shambles to another". Shadow immigration minister Chris Bryant said: "This Government's usual level of incompetence is not good enough when it comes to our borders."

Mr 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 union action."