More than 100 Post Office branches and hundreds of head office jobs are at risk as part of a radical shake-up of the business, the BBC understands.
Under the plan, 115 loss-making branches wholly owned by the Post Office could be closed.
The Post Office is looking at options including alternative franchise arrangements where another operator or third party could take on the branches instead.
These sites employ around 1,000 workers. In addition to this, hundreds of jobs are under threat at the group’s headquarters.
The Post Office’s new chairman Nigel Railton will brief staff on Wednesday on the outcome of a review launched earlier this year.
The former boss of Camelot was appointed interim chairman of the Post Office after his predecessor Henry Staunton was sacked in January.
The aim of the review is to put the Post Office on a firmer financial footing.
The troubled organisation is currently the subject of a long-running inquiry into the Horizon IT scandal, in which hundreds of sub-postmasters were wrongly prosecuted after faulty software made it appear money was missing from their accounts.
Railton has already told the Post Office inquiry that a new deal was needed for sub-postmasters, to put them at the centre of the business.
The strategic review is designed to fundamentally change how the Post Office operates.
The business has 11,500 Post Offices across the UK, most of which are franchises.
Of this number, 115 are Crown Post Offices in city centres staffed by Post Office employees.
Earlier this month Post Office minister Gareth Thomas said the organisation was at a critical juncture and the government had already commissioned its own review into what the Post Office should look like in the future.
Business Secretary Jonathan Reynolds told the inquiry on Monday that he didn’t feel sub-postmasters were getting appropriate pay for the amount of business they conduct.
He hinted that Post Office branches could step into filling the gap left by High Street bank branch closures.
Ministers have been exploring plans to hand ownership of the Post Office to sub-postmasters.
Reynolds told the Horizon inquiry there was still “tremendous affection” for the Post Office among the UK public and a “desire for it to have a strong future.”
He said the Post Office “has to be one that has a significantly smaller centre” and sub-postmasters needed better pay, adding “that will necessitate some quite considerable changes to the organisation centrally to do that”.
A Post Office spokesperson said that on Wednesday the organisation would be setting out a “new deal” for postmasters and for “the future of the Post Office as an organisation”.
“It will dramatically increase postmasters’ share of revenues, strengthen our branch network and make it work better for local communities, independent postmasters and our partners who own and operate branches,” he added.