Members of the Communication Workers Union (CWU) at so-called Crown offices will walk out for 24 hours - the ninth round of industrial action since Easter.
The union is opposed to plans to close or franchise 75 Crown offices - the larger branches usually sited on high streets - saying that services and jobs will be affected.
Dave Ward, CWU deputy general secretary, said: "It's becoming ever clearer that the Post Office is obsessed with cost-cutting, closing post offices and slashing jobs and local services.
"This is being done against the wishes of customers and communities and with no political mandate. It is a shocking robbery of local services and misuse of public money - with £15.4 million paid out in bonuses to senior managers while frontline staff face job losses and pay freezes.
"Our members' determination has been unwavering because they know they are right. They are standing up to protect jobs, services and for a fair pay rise.
The Post Office said the 370 Crown branches were losing £37 million a year and had to be brought into profit, adding that it was proposing to franchise 70 branches with retail partners, and invest around £70 million in 300 branches.
Kevin Gilliland, the Post Office's Network and Sales Director, said: "We regret any inconvenience caused by this strike action. We will be working hard to minimise disruption to customer service.
"We must continue with our plans to turnaround the Crown network to ensure we keep these branches on high streets and in city centres across the UK. We remain open to discussions with the CWU on pay options which do not add to the current loss of public money."