The National Federation of SubPostmasters, representing Royal Mail staff running thousands of local Post Office branches, called on its members to deliver a massive snub to the government's plans by refusing to put up material explaining to the public how they could buy shares in Royal Mail.
The NFSP has been fiercely against the move, branding it "catastrophic" and a "reckless gamble" that could force thousands of branches to close.
General secretary George Thomson said: “The Government’s failed its pledge to make post offices the ‘front office for government’. We are more dependent than ever on Royal Mail services.”
"I am surprised and angered by Post Office Ltd's request for subpostmasters to act against their own interests by encouraging the public to back the sale by buying shares.
"I know how tough our members are finding it to keep their Post Offices open due to cuts in their pay and the withdrawal of key services, and the payment which Post Office Ltd will offer for stocking these materials may be appeal ing. However, I am confident members will support our call not to stock the share prospectus."
A Post Office spokeswoman said: "This is a matter for government and no decisions have been made yet [over stocking the prospectuses and materials]."
This comes after the Department for Business confirmed it would be launching a massive advertising campaign using public money to promote the Royal Mail sale once it is launched onto the stock market later this financial year.
The stock market flotation, expected for March 2014, would see the Royal Mail valued at a potential £3 billion and 10% of its shares handed to Royal Mail staff.