Royal Mail managers will walk out on the postage firm later this month amid a dispute over jobs and pay.
Unite said that 2,400 managers will work to rule on July 15-19, followed by strike action on July 20-22.
Union officials have accused bosses of ‘greed’ and ‘profiteering’ in their announcement on industrial action.
The Royal Mail is said to be planning to cut 542 frontline delivery managers' jobs alongside a redeployment programme to bring in worsening terms and conditions.
The firm said that it was ‘disappointed’ by the move made by managers to strike.
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Unite general secretary Sharon Graham said: “This business is awash with cash but it is putting profits and dividends for the few at the top ahead of its duties as a public service.
“There is not a single aspect of these cuts which is about improving customer service. They are being driven entirely by a culture of greed and profiteering which has seized a 500-year-old essential service, driving it close to ruin.
“Our members are determined to force the business to take a different path, and they have the full backing of Unite.”
A Royal Mail spokesperson said: “We are disappointed that Unite has notified us of planned industrial action. There are no grounds for industrial action.
“The extended consultation on our recent restructure concluded earlier this year, and the restructuring is complete.
“We committed to protecting pay for all managers who stay with Royal Mail, and the vast majority have seen an increase in their earnings.
“We allowed managers to request voluntary redundancy with a package of up to two years’ salary, which was over-subscribed. We also made several concessions during the process, which Unite declined.
“We have contingency plans in place to minimise disruption for customers in the event of industrial action, and we will work to keep people, businesses and the country connected.”
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