Of the 112,000 CWU members that received ballot papers last month, 74% responded and of those 92% voted yes in response to the question ‘Do you support the boycott of competitors’ mail?’
A CWU spokeswoman told PrintWeek that it was not a ballot for industrial action and that the union would continue to negotiate with Royal Mail.
She added: "Ideally we would want to sit down and work on negotiations to reach a resolution first. Direct action is always the absolute last resort and we will do what we can to resolve this first but if we do enter negotiations and they are unsuccessful then it would most likely be sometime during the summer that we would start announcing dates for action."
CWU deputy general secretary Dave Ward said: "Royal Mail workers have shown they understand the threat to the universal service from unfair competition and the race to the bottom on their own terms and conditions. The way competition is being introduced does not benefit customers, small businesses or postal workers in whatever company they work for."
In a statement issued in response to the ballot results Royal Mail said that a boycott would be against the law.
It said: "Royal Mail believes that any direction by the CWU that postmen and women should refuse to handle access letters and parcels would be unlawful.
"Royal Mail operates in a very competitive market and customers can move their business very quickly. This could result in a significant loss of business."
The ballot, which aimed to bolster the union’s lobbying efforts to improve workers pay and conditions, posed four questions in total.
Of the remaining three, 96% of respondents opposed the privatisation of Royal Mail, 92% supported the CWU Pay claim and 92% supported a policy of non-cooperation.
Ward accused the government and Royal Mail of alienating the workforce and called for "serious negotiations to find a solution", otherwise he warned that prolonged industrial conflict was inevitable.
He said: "This ballot result is a damning rejection of the tired old government privatisation policy and the actions of the Royal Mail board in support of this. Postal workers have worked incredibly hard to turn the fortunes of the company around. Royal Mail is not a financial basket case and they know privatisation is only benefitting vested interests.
"Postal workers are not going to sacrifice their souls for a so-called 10% stake when they know their jobs, pensions and conditions are once again under threat."
Royal Mail’s statement said: "Royal Mail notes the outcome of the CWU consultative ballot and is committed to seeking an agreement with the union on the way forward that equips the business for the future and is fair to our employees."
Ofcom declined to comment on the results of the ballot.
