British border agents are set to go on a one-day strike just before the start of the London Olympics, which could mean major delays for thousands of visitors headed to the games.

The Public and Commercial Services (PCS) union announced Thursday its members, who include passport officials, would stage a 24-hour strike on July 26 in a battle over job cuts and pay.

Home Secretary Theresa May said the decision to stage a strike on the eve of the London Games was "shameful." She said the government would "put contingency arrangements in place to ensure we can deal with people coming through the border as smoothly as possible."

The union also said its members would refuse to work overtime until Aug. 20, which includes the Olympic period from July 27 to Aug. 12. PCS has 16,000 members working in the Border Agency, the Identity and Passport Service and the Criminal Records Bureau.

The union has been upset over the government's cuts and layoffs, which it blames for causing “chaos at the borders and queues at airports.” A report this week by the U.K. National Audit Office said the Border Agency had laid off 1,000 more staff than it should and was having to hire extra people and increase overtime.

Immigration Minister Damian Green called the union action "a selfish and irresponsible act", noting that only a fifth of the membership had voted on the ballot.

Green told BBC News he was confident there would be minimal disruption at the immigration desks because extra staff from the Home Office and other departments had already been trained to cover.

The announcement comes on the heels of a major embarrassment the Games organizers suffered earlier in the week when security contractor G4S PLC admitted it would been unable to deliver on its promise to supply about 10,400 guards to help keep the Games safe — a last-minute admission that has forced the government to call in 3,500 soldiers to help meet the shortfall.

Olympics Secretary Jeremy Hunt acknowledged Thursday that even that may not be enough, telling the BBC that the government put an extra 1,200 troops on standby "in the unlikely situation that G4S's performance deteriorates from where it is today."

"We want to ensure the public against every eventuality," he told Sky News earlier. "We don't expect to use them, but they will be there."

Among the issues the union is fighting over are:

• Compulsory redundancies.
• Government plans to cap pay increases at 1 per cent for the next two years.
• The use of private companies to deal with the backlog of immigration and asylum cases.

In fact, the Games could be beset with plenty of labour trouble.

Also on Thursday, 400 train workers threatened to strike for three days in central England during the Olympics in a pension dispute. Drivers for East Midlands Trains said Thursday the strike would be from Aug. 6 to 8.

The strikes could be highly disruptive to the Games — Olympic soccer matches are being held across the U.K., many workers are coming from outside London and thousands of spectators will be using trains to get to venues around the capital.

Sources: News reports, Heathrow airport, LOCOG
With files from The Associated Press