Hundreds of jobs are being moved out of the city centre as one of the city centre's biggest employers plans to close a major site near Pennycomequick.
The Royal Mail plans to close the Manual Data Entry Centre (MDEC) "as soon as possible" - and The Herald understands that could mean as early as August.
Bosses say the transfer of up to 350 staff will have "no negative impact on mail service in Plymouth".
Details of the plans were revealed in the recent Plymouth and South West Devon Joint Local Plan, which is a blueprint for the future of the city and potential developments.
The council has earmarked the site for conversion into 141 new homes - but says the imposing building should be renovated rather than developed.
Student flats could be on the cards - wtih a major block called Central Park Towers next door and the planned £40million redevelopment of the neighbouring railway station expected to include some university accommodation.
It is understood that many current employees will be moved to another Royal Mail sorting and delivery office in Plymstock, which already employs up to 450 people.
In its heyday, as many as 850 people were based at the Pennycomequick HQ.
"Whilst staff will be moving, no jobs will be lost," Ralph Ferrett, branch secretary of the Plymouth and East Cornwall Communication Workers Union (CWU), told The Herald.
"There will be some sadness about losing a historic Royal Mail building, but we are confident that our members concerned have been addressed and that there will be no negative impact on mail service in Plymouth.
"We are unaware of any set date for the move, but we understand that they are looking to start ASAP."
Mr Ferrett added: "We weren't directly aware of any future plans but the site is located in a prime location
in the city centre, which would be extremely valuable to property developers.
"Nobody will be made forcibly redundant because of the move."
However, Mr Ferrett said there could still be cuts as part of wider Royal Mail initiatives.
A spokesman for Royal Mail told The Herald "We constantly keep all our operations under review in order to ensure we are properly equipped to respond to continued structural decline in mail volumes, a growth in parcel traffic and increased competition."
"Any changes will always aim to improve customer service and minimise disruption to our people."