On 27 September ballot papers will be sent to 115,000 postal workers in the Royal Mail and Parcelforce, with the results to be announced on 16 October. Post Office staff are excluded.

Strike action could then commence from 23 October, following a seven-day legal notice period to Royal Mail.

The ballot was originally supposed to take place today (20 September), with results due to be announced on 3 October and industrial action possible from 10 October, however the union said the ballot had been delayed due to logistical details.

Open-ended negotiations are still ongoing between Royal Mail and the union. A spokesman said: "Really we still want to reach an agreement, industrial action is a last resort, but I think finding a resolution in this time scale is extremely unlikely."

Last week a union spokeswoman confirmed that the organisation was consulting lawyers about how it could include a boycott of DSA providers as part of planned industrial action.

The union is in dispute with Royal Mail over pay, pension and contractual terms as well as last week’s confirmed privatisation of the national postal organisation. The Royal Mail has proposed a three-year legally-binding agreement that includes an 8.6% pay increase.

But the CWU has rejected the proposal, which it claims was linked to accepting major pension changes and a no strike deal. It is demanding an above inflation, no-strings pay deal.

CWU deputy general secretary Dave Ward, said: "The government’s privatisation agenda has destabilised everything. Postal workers are rightly concerned about their future so we want a legally-binding agreement on protections for jobs, terms and conditions – regardless of who owns the company.  Without an agreement strikes are inevitable."

"We want the company to recognise its main asset – its workers – who literally deliver the success of the business. This union still wants an agreement and we are hoping this strike ballot will focus the minds of Royal Mail and bring us to a legally binding deal that will protect the interests of postal workers for the long-term foreseeable future."

He added: "Attacks on terms and conditions and the threat of new employment models in a potential race to the bottom with competitors are a real risk for postal workers and we intend to achieve legally binding protections that mean the future of postal workers jobs are secure and Royal Mail continues to set the benchmark for pay and conditions in the postal industry."