Over 97 percent of votes from members of the Communication Workers Union (CWU) backed action. The turnout was 76 percent. Most of the staff agreed to walk out in what they said a "fight of our lives".
Around 110,000 members voted on whether to launch the campaign of industrial action before the outcome was announced on Tuesday.
Strike dates are not yet announced at this moment, but the union is expected to target the annual Black Friday retail sales event in late November and the Christmas post.
The CWU said that Royal Mail, a 503-year-old company, is not honouring an agreement reached last year covering a wide range of issues, including plans to reduce the working week, as well as job security.
Union bosses fear the company is trying to scrap rules which means it must deliver to every address in the UK six days a week for a set price.
They say dropping to a five-day week would cost 20,000 jobs but the company denies any plan to do so, according to local media reports.
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