Royal Mail's chief executive, Moya Greene, has ordered a snap cull of delivery office managers as part of her latest round of cost cuts to get the company ready for privatisation.
Managers were told on Friday that all those who had volunteered for redundancy would leave by the end of this month apart from a minority the company wants to keep.
Departing managers will be paid their 12 weeks' notice as well as their redundancy terms in an apparent show of decisive action after Royal Mail posted a loss last week.
The cuts are said to cover all management grades on permanent contracts with the group. It is unclear how many will be affected.
No compulsory managerial redundancies have been made so far, but a further swathe of managers were declared "surplus" and will be moved to fill vacancies in other offices in a process known as "bumping".
A Royal Mail spokesman said: "Royal Mail is in a difficult financial position. Mail volumes have fallen by more than 20% in the last five years and are forecast to fall by around 5% a year in the future. We have made clear the company will be smaller in future as a result of volume declines. This is irrespective of any moves on privatisation.
“We announced in March we would be consulting Unite/CMA on reducing operational managers by 1,000 through voluntary means. This followed a separate review which means 1,700 non-operational managers in head office departments are leaving. As part of this process, some managers who had applied for voluntary redundancy were told last week their applications had been accepted.
“There has been no new job reductions announced. It remains our policy to first tell our colleagues and the unions about any developments affecting people in the company.
“Since 2002, 45,000 people full time equivalent people have left Royal Mail Group."
The sudden move is said to have been taken without consulting the Communication Managers Association union, which was taken by surprise. The union, which represents Royal Mail's rank and file, is already considering industrial action to fight the plan.
Ms Greene ordered area managers to tell staff of the latest cuts by Friday.
She warned publicly last week that more cuts were on the way after Royal Mail's letters division posted a loss of £120m for the last financial year. This sent the group to a £49m loss for the year from a £113m profit the year before.
Friday's job reductions show Ms Greene's cuts digging into managerial posts. The group announced in March that it intended to reduce the number of operational managers it employed by 1,000 through a programme of voluntary redundancies.
Ms Greene, the former head of the Canadian postal service, was parachuted into the top job at Royal Mail to get the company in shape for a sell-off that could be delayed until she turns performance around. She made £637,000 in pay and bonuses last year.