Members of the Communication Workers Union will walk out for half a day from 12.30pm, the eighth round of industrial action since Easter.
The union is campaigning against plans to franchise or close 75 of the Crown offices - the larger branches usually sited in high streets - saying it will hit jobs, and adding that staff have not had a pay rise for more than two years.
CWU deputy general secretary Dave Ward said: "Post Office plans to close offices, cut jobs and reduce services cannot go on unchallenged. It's time that Government stood up for these highly-valued local services which their constituents are signing petitions for in their tens of thousands. We are calling on chief executive Paula Vennells to now lead talks to resolve this.
"Our members are taking a strong stand with this latest, eighth round of strike action. Their 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 company is in disarray and clearly out of touch with both its staff and customers."
Tens of thousands of people have signed petitions against the plans.
The Post Office has argued that the Crown offices are losing money, adding that most of the 75 will be moved to other stores under franchising arrangements.
Kevin Gilliland, network and sales director at the Post Office, said: "We are disappointed at the CWU's decision to call further strike action. This can only cause disruption to customers and cost our people money.
"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."