Royal Mail staff voted overwhelmingly in favour of going on their first strike in a decade.
Over 97% of votes by members of the Communication Workers Union backed a strike. The turnout was 76% (around 110,000 UK postal workers).
The result was the largest yes vote for national industrial action since the passing of the Trade union Act 2016.
Workers were unhappy with the firm regarding issues such as job security and their terms and conditions of employment.
The Act determines that a majority of those balloted must return their ballot paper, with the high threshold usually blocking trade unions from taking industrial action.
The CWU previously beat the threshold in 2017, and has now done so for second time. The CWU is the only trade union in the UK to have passed the threshold.
Deputy General Secretary (Postal) Terry Pullinger said: “Just over one year ago the Royal Mail Group Board and the CWU agreed a blue print agreement for the future, a progressive agreement that included an historic pension solution, a mutual interest driven relationship and a joint vision for a successful postal service with social aims.
“Today the new RMG leadership are breaking that agreement. Our members take honour seriously and have voted to fight for that agreement against those who now seek to break up the great British Postal service in the interest of fast track profit and greed. Integrity and pride still matters and we will not stand aside and see what we have spent our working lives building destroyed.”