The threat of a post strike in the run-up to Christmas has been raised as over 100,00 postal workers prepare to vote on industrial action over issues linked to the Government's controversial plans to privatise the Royal Mail.
The Communication Workers Union said 125,000 of its members will be balloted over pay, jobs, pensions and the impact of any sell-off, with industrial action possible from October 10.
The move is a major challenge to the planned privatisation, although the Government said it will not alter its decision to sell shares in Royal Mail in this financial year. The Royal Mail said industrial action, or the possibility of disruption, was damaging to the business, especially in the run-up to Christmas - its busiest time.
But the union warned a strike was "inevitable" unless a deal was agreed on a number of issues, including pay, further changes to workers' pension scheme, the impact of possible privatisation on job security and terms and conditions, and the company's future strategy.
All Royal Mail and Parcelforce workers in the CWU will be balloted from September 20, with the result due on October 3. If there is a yes vote, the union would have to give seven days' notice for strike action.
Dave Ward, CWU deputy general secretary, said: "We are dealing with a company that is preparing for privatisation with relish. While the union continues to fight privatisation we are also dealing with the potential realities for workers if there is a change of ownership.
"We are looking to reach a groundbreaking agreement on terms and conditions that sets unprecedented legally binding protection for workers in the event of a sale, and regardless of who owns the company.
"Postal workers know franchising, break up and sale of mail centres, distribution hubs and Parcelforce, along with the introduction of a new workforce on lower terms and conditions, are real threats in a race to the bottom with mail competitors for any new company. We want Royal Mail and the government to put protections in place that are both meaningful and lasting."
A Department for Business spokesman said: "Industrial action is not necessary. It is disappointing that the CWU leadership has decided to ballot for strike action.
"They are standing between their members and a generous pay offer of 8.6% over three years, which is more than teachers, nurses and our armed forces, who have had pay increases capped at 1%. Royal Mail management are continuing to talk to CWU and we encourage both sides to resolve this dispute."