About 130,000 postal workers are to be balloted on strikes in a row over pay, threatening the first national walkout in a decade.
The Communication Workers Union (CWU) rejected a 2.5% offer and agreed a timetable for the ballot, which will start later this month.
The union said the Royal Mail's business plan would lead to 40,000 job losses, a pay cut for postal workers and the closure of mail centres and delivery offices.
The union's deputy general secretary, Dave Ward, said: "Royal Mail has abandoned our agreed approach in favour of a short sighted business plan that amounts to a cost cutting frenzy, reductions in pay and a defeatist attitude towards competition.
"This business plan is designed to fail and demonstrates a real lack of vision by the people running the company.
"Royal Mail's business plan will result in 40,000 job losses, attacks on pension arrangements, closures of mail centres and delivery offices and a reduction in pay for postal workers to 'the market rate'. It will also result in a reduction and decrease in quality of service for the public."
Ballot papers will be sent out on May 22 and the result will be announced on June 7 at the union's annual conference.
A Royal Mail spokesman said: "For the union to demand a 27% increase in pay and a shorter working week - at a cost of £1 billion - is madness given Royal Mail already pays its people 25% more than its rivals pay and is 40% less productive.
"To call for strike action when we are already rapidly losing market share to those rivals is also insane and shows that the union has no understanding of the very tough commercial environment we are operating in."
The last national postal strike was in 1996.
