Members of the Communication Workers Union (CWU) served its required notice to Post Office Ltd last night stating the intention to strike, following an 88% vote in favour of strike action and, according to the union, a refusal from the Post Office to negotiate.
The workers on strike will be the 4,000 staff working in the network of 373 Crown post offices - the outlets owned and run by Post Office itself, rather than franchisee subpostmasters. The post offices handle about 20% of all Post Office business.
The action is in protest at plans to close or franchise more than 70 Crown offices, as well as over pay and jobs.
The union said Post Office staff have not received a pay rise since April 2011.
CWU deputy general secretary Dave Ward said: "With Post Office management refusing to negotiate, and with such a huge vote in favour of strike action, we have had no choice but to serve notice for strike action.
"The patience and loyalty of our Post Office members has been abused by Post Office management. This dispute is about protecting jobs and services as well as securing a fair pay increase for our members. We're saying to the public 'If you value your post office, support these workers on Easter Saturday and beyond'."
Last month, the Post Office announced it wanted to close up to 70 Crown offices and replace them with franchises based in other shops. Crown Post Offices, usually based in high streets, are currently losing £40m a year.
The union also said it wanted to secure a pay rise for crown office counter staff, who have not had one since 2011, unlike other workers such as supply-chain staffers and postmasters.