Royal Mail postal workers have voted to take strike action over job security and working conditions.
They voted three to one in favour of action, with 61,623 out of a total of 80,830 workers who voted saying they wanted to strike.
But the Royal Mail said 60% of the total number of postal workers working in the UK did not vote to strike.
The company and unions have been unable to resolve differences on how best to modernise the postal service.
The Royal Mail "condemned" the plan to strike as "deplorable and irresponsible", saying it would drive away customers and undermine confidence in the postal service.ANALYSIS
By Martin Shankleman, BBC employment correspondent
The outcome may not have been in doubt, but the size of the majority in favour of action is certainly a surprise.
Three quarters of union members polled endorsed the union's call for a national stoppage - much higher than expected - at a stroke undermining the Royal Mail's suggestion that staff disaffection with the company was restricted to a few hotspots around the country.
It is also significant that the government, which owns the business, has refused to intervene, despite fresh pleas today from the CWU leader Billy Hayes.
But given his union's role in destroying Labour's plan to part-privatise Royal Mail in the summer, it's hardly surprising that his union has few, if any, friends left in Whitehall.
"It is clearly reprehensible for the union to continue to hold strikes when Royal Mail is not planning any further efficiency changes for the rest of the 2009 calendar year," said the company's managing director Mark Higson.
He called on the Communication Workers Union (CWU), which conducted the strike ballot, to stop the strike and return to the negotiating table.
The Royal Mail said 121,000 members were balloted, but there are a further 20,000 postal workers who are not members of the union.
'Death wish'
Dave Ward, deputy general secretary of the CWU, said his union would meet next Monday to agree its next step and would work hard to avoid a strike. He said it would give the Royal Mail a "final opportunity" to resolve the dispute over the next 10 days.
He added that union members had delivered a "damning verdict on the way the Royal Mail is run. We understand the need for modernisation, but it needs to be done in a way that protects workers".
Mr Ward also said the government had "caused many of the problems" the Royal Mail was now experiencing.
"If we don't take a stand now, postal services in the UK will be destroyed forever," he said.
Postal Affairs Minister Lord Young said: "A national postal strike is completely self-defeating and will only serve to hurt consumers and businesses who rely on the post and drive even more people away from using mail as a means of communication.
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"Royal Mail must modernise and these strikes will slow down that essential process."
He called on the CWU to "do more" in its negotiations with the Royal Mail and said that strike action would simply lead to more jobs being lost.
The British Chambers of Commerce (BCC) also criticised the vote in favour of a strike, describing it as "akin to a death wish".
"This strike announcement defies logic at a time when businesses and government are working hard to move the UK economy back to growth. Postal delays are already hurting small businesses and major companies across the country," said Dr Adam Marshall, director of policy at the BCC.
Businesses have expressed concern about a strike, particularly in the run-up to the important Christmas trading season.
In order to help small businesses, eBay said it would temporarily remove the option for buyers to rate sellers on the time taken to dispatch an item.
Modernisation
Royal Mail made an operating profit of £321m in the year to 31 March, but it was the first time in 20 years that all four parts of the business had been profitable.
The company says the number of letters and parcels its core business delivers is falling by 10% each year, losing it £170m per annum.
One major reason for this is increased competition from electronic forms of communication such as e-mail.
Both the Royal Mail and the CWU agree that job cuts are needed as part of a vital streamlining of the mail service to cope with the drop off in postal deliveries.
But the CWU says Royal Mail managers are refusing to meet its demand for a signed agreement determining the scope of cuts, as well as job and pay security guarantees for those workers who will ultimately remain in their jobs.
The Royal Mail says that by signing up to an agreement after the last national postal strike in 2007, the CWU accepted the future job cuts it needed to make in order to modernise the service.