The Communication Workers Union (CWU) warned the 24-hour strike could be followed by more industrial action.
The workers will be joined by more than 700 Post Office managers who are members of the Unite trade union.
Dave Ward, general secretary of the CWU, said: “The Post Office is relentlessly pursuing a programme of cuts that will mean a further 2,000 job losses, staff being left tens of thousands of pounds worse off in retirement and the privatisation of its flagship branches.
“The Post Office is at crisis point and the government has to step in.”
The Post Office said it was ‘disappointed by the call for industrial action’, but said that contingency plans would minimise disruption to services during the strike.
Kevin Gilliland, Post Office’s network and sales director, said 97 per cent of its 11,600 branches would operate as normal.
“We will also work hard to minimise any disruption to customers in our 300 Crown branches should they be affected by strike action,” he said.
The CWU has about 3,500 members working for the Post Office, including counter staff at the 300 Crown branches.
It also has members who deliver cash to rural branches and said it was confident the strike would therefore affect the majority of the Post Office’s branches.
Mr Ward added: “We are making a simple demand.”
“The government needs to pause the cuts, convene a summit of key stakeholders in the industry and work out a strategy that gives employees and the public confidence that the Post Office has a future.”
Mr Gilliland said: “The changes are needed to make our services better for customers and ensure that Post Office branches thrive at the heart of communities for future generations.
“We halved our losses in 2015/16 and are making steady progress to reduce costs to the taxpayer by making our business simpler to run and modernising our network, which is now at its most stable for decades.”
A department for business spokesman said the Post Office’s financial performance continued to improve and the network now had more than 11,500 branches, with 3,500 open on Sundays.
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