Postal workers are to be balloted for national strikes 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 vote in the coming weeks over pay, jobs, pensions and the impact of any sell-off, with the result due in early October.
The first strike could be held on October 10 if there is a yes vote. The move is a major challenge to the planned privatisation, which ministers are expected to press ahead with in the coming months.
The union warned a strike was "inevitable" unless a deal was agreed on a number of issues. The CWU is in dispute over a pay claim, 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. Royal Mail continues to prepare for privatisation with relentless rounds of budget cuts in offices across the UK. There is no understanding that the pace of change can really only be led by how hard people can work, and CWU members are being driven to absorb absences, carry increasing amounts of mail and work harder than is possible in many cases.We have reached breaking point, particularly in delivery offices, and the culture has to change."
It will be the first national postal ballot since a pay and conditions dispute in 2009. The union said it had rejected a below-inflation pay offer linked to accepting major changes to working conditions and pensions.
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."
A Royal Mail spokesman said: "Royal Mail is very disappointed that the CWU has issued a timeline for a national ballot for industrial action, if an agreement is not reached in on-going talks. Discussions over a new three-year agreement between Royal Mail and the CWU are continuing. We are committed to reaching an agreement with the CWU as soon as possible to give our customers and employees continued stability. We believe that focusing on the possibility of industrial action is inappropriate."