More than 100,000 Royal Mail workers are to be balloted for strikes over issues including job security and terms and conditions of employment.
Members of the Communication Workers Union (CWU) will vote from September 24, with the result due in the first week of October.
The dispute has flared over implementation of a so-called Four Pillars Agreement reached last year between the union and Royal Mail.
The union said in a statement: “In setting this timetable we clearly believe that the business, in spite of their own media campaign, are not working within the spirit and intent of our national agreements and are following their own agenda that will have long-term detrimental effects on our members’ terms and conditions of employment, job security and the future of Royal Mail Group as a whole.”
The union has claimed that a culture of bullying in the workplace had not been tackled, with local CWU officers being disciplined.
Deputy general secretary Terry Pullinger told a CWU meeting that members should get ready for the “fight of your lives.
The agreement was one of the final acts of former chief executive Moya Greene, and covered pay rises, new pension proposals and moves to reduce working hours from 39 to 35 a week by 2022, subject to productivity improvements.
Since Rico Back took over as chief executive last year, a culture of bullying has increased, according to the CWU.
Unofficial walkouts are now running at more than one a week, including in small, rural offices not noted for militancy, said a CWU source.
The union has also voiced concern about the company’s recent decision to move its Parcelforce business to a separate legal entity.
Shane O’Riordain, from Royal Mail, said: “We have not received formal notification of a ballot from CWU. We are disappointed that they have set out a ballot timetable while discussions are ongoing.
“We are committed to open and constructive engagement with the CWU. We all want a successful and sustainable company that provides good quality jobs, fairness in workloads, and continues delivering the Universal Service.”
The company said it was honouring the 2018 agreement, awarding two pay increases of 5% and 2% and granting the first hour’s reduction in a shorter working week, even though it only generated some of the savings to pay for it.
Royal Mail added it had worked with the CWU to lobby Government for a new pension scheme and plans to invest around £1.8 billion in the UK over the next five years as part of its transformation plan aimed at returning the UK business to growth and underpin the Universal Service.
The CWU said that while it had spelt out the timetable for the ballot, it still provided a period of weeks for further dialogue/external mediation to try and secure a final settlement on honouring the commitments detailed in the Four Pillars Agreement and all associated issues before the ballot process starts in late September.