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.