UK Border staff are to strike the day before the Olympics Opening Ceremony, bringing the threat of long queues at Heathrow immigration desks as officials, athletes, dignitaries and tourists arrive in London for the games.
The day of the strike is the peak arrivals time for sponsors and international media.
The Public and Commercial Services Union, whose members are Home Office staff including border officials, voted for the strike. The Union's general-secretary Mark Serwotka, pictured right, has confirmed the one-day strike will go ahead. For the rest of the Olympic period a work-to-rule and a ban on overtime will be in place.
David Cameron, who is in Afghanistan, said: "I do not believe it will be right. I do not believe it will be justified."
Union leaders say the strike is in protest at "public service falling apart at the seams", as thousands of job cuts, pension reform and pay freezes loom over much of the public sector.
Hours before the strike was called, Culture Secretary Jeremy Hunt, who has ministerial responsibility for the Olympics, said a strike "would be out of tune with the British public. The unions will lose huge amounts of public support if they try to do this. The vast majority of the public want a successful games". Border staff went on strike in May, and it didn't lead to a significant increase in the sort of queuing problems at Heathrow that, with the games looming, had already made headlines around the world. But the unions claim the staff that were brought in to replace them didn't check passports properly.
In contrast to the industrial action, hundreds of Whitehall staff, including many from the Home Office, have taken annual leave to work as some of more than 70,000 volunteer "gamesmakers". Hundreds of volunteers are also working unpaid at Heathrow, a crucial part of Olympic infrastructure plans.
One gamesmaker at Heathrow told The Independent: "It's incredibly disheartening. A lot of us who volunteered naturally wanted to be at the Olympic Park, but I'm still very proud to be here, doing my bit. I'm sure it'll all work out fine, and I'm not making light of their issues, but why do it now? It is childish in the extreme."
Drivers on East Midlands Trains are also to stage a three-day strike from 6 August and members of the RMT on South West Trains have voted to take industrial action short of a strike in a dispute over an Olympic bonus.
Earlier this week, London bus workers were awarded a bonus, despite the majority of routes being unaffected.