Len McCluskey, the head of the Unite union, suggested its members could stage walkouts during the 2012 Summer Games to oppose the Conservative-led government's sharp austerity cuts. The union says it represents 200,000 public sector workers.
He was quoted as telling The Guardian newspaper that the July 27-Aug. 12 London Olympics are a justified target for those opposing spending cuts and job losses.
"It is completely unacceptable and unpatriotic what he is proposing," Cameron's spokesman Steve Field told reporters. "Most people in this country, including members of that union, think the Olympics is a great occasion for the country and wouldn't want to see anything happen that would disrupt it in any way."
Both Cameron and Ed Miliband, head of Britain's main opposition Labour Party — which receives significant financial backing from Unite — condemned the threat of industrial action.
"Any threat to the Olympics is totally unacceptable and wrong," said Miliband. "This is a celebration for the whole country and must not be disrupted."
Cameron urged Labour to turn down money from the union in response to its Olympic threat.
McCluskey said that no plans had yet been drawn up for specific action during the Olympics but that any activity could "absolutely" include strikes.
"I believe the unions, and the general community, have got every right to be out protesting," he was quoted as telling the newspaper. "If the Olympics provide us with an opportunity, then that's exactly one that we should be looking at."
He said that the "idea the world should arrive in London and have these wonderful Olympic Games as though everything is nice and rosy in the garden is unthinkable."
John Armitt, the chairman of the Olympic Delivery Authority, urged Unite not to take action. "Len and his colleagues have a right to make their point, but I hope they don't feel the need to disrupt other people's pleasure during the summer," he said.
In November, George Osborne, Britain's Treasury chief, announced 23 billion pounds ($37 billion) of additional spending cuts through 2017, extending a planned four-year program of 81 billion pounds ($129 billion) of budget trimming. He also capped public-sector pay rises at 1 percent for two years.
Britain's independent Office for Budget Responsibility estimates job losses in the public sector will reach 710,000 by early 2017, a rise from a previous forecast of 400,000 by the first quarter of 2016.
An estimated 2 million public workers — including paramedics, teachers and even some employees from Cameron's office — joined the country's largest strike in decades last November to draw attention to government cuts.