Postal workers have voted to go on strike in a row over post office closures, job cuts and pensions, the Communication Workers Union (CWU) has announced.
The union said the Post Office was "on the path to extinction" as the ballot saw an overwhelming majority of 83.2% vote in favour of industrial action.
Dave Ward, CWU general secretary, said: "Staff in the Post Office face 2,000 job losses this year, the closure of their pension scheme and a strategy of slash and burn from the board of the company.
"The Post Office is at crisis point and the Government has to step in."
Around 3,500 CWU members in Crown offices, supply chain depots and administration sites across the UK were due to be balloted on strike action, the union said ahead of the vote.
It was said to be the first time workers from different parts of the business were being balloted together.
The planned industrial action comes amid concerns that public funding for the Post Office has been withdrawn, revenues have stalled and that staff and customers are "paying the cost", the union said.
"We have a very simple demand," Mr Ward said.
"The Government has to step in, convene a summit of key stakeholders and hammer out with us and the board a strategy that will give the Post Office a future. It cannot wash its hands of this and simply stand by as a national institution goes under.
"Just as we have seen with Tata Steel, this is another clear example of the Government having no plan whatsoever to stand up for British industry."
But the Post Office said only half of CWU members had participated in the ballot, meaning just 41% of members had voted in favour of the strike.
The service branded comments by the union about its performance as "misleading" and said they would "cause undue concern for customers and employees".
It said it had halved losses in 2015/16 and was making "steady progress" in reducing costs to the taxpayer.
Kevin Gilliland, network and sales director, said: "We must continue with our plans to modernise our network and make it better for customers. We are taking the right actions to ensure that Post Office branches thrive for future generations."
The Post Office said 97% of its network of 11,600 branches would not be involved in any industrial action, but added that it would work to minimise disruption in those affected.
The company called for "continued dialogue" with the CWU following the ballot.
"We will give serious consideration to any ideas that our unions put forward to help us create the Post Office network that our customers need for the future, and urge them to continue to work with us," Mr Gilliland said.
"We are happy to talk and continue to invite the CWU to join us at the negotiating table."