A union has raised concerns over the future of its members who work in post offices operating inside WH Smith shops.
WH Smith is in talks over a potential sale of its High Street stores as the business has become more focused on its shops in airports and service and train stations.
This has raised questions over the future of 195 post offices housed within the High Street stores. The Communication Workers Union (CWU), which represents Post Office staff in the shops, warned any potential closures would be "devastating".
A spokesman for the Post Office told the BBC the company remained in contact with the retailer over its plans.
Since news of WH Smith's potential High Street stores sale emerged over the weekend, the BBC has been contacted by many people asking about the fate of post offices within the stores.
WH Smith has said its High Street stores remain a "profitable and cash-generative part of the group", and it is exploring various options, "including a possible sale".
It added: "There can be no certainty that any agreement will be reached, and further updates will be provided as and when appropriate."
The BBC understands the commercial relationship between both the retailer and the Post Office is strong, with benefits for both parties, therefore any new potential buyer might maintain the current arrangement.
The announcement comes amid a difficult economic outlook for High Street retailers.
The first of WH Smith's 500 stores opened more than 230 years ago, operating as a news vendor. It has since grown into a major High Street and travel retailer.
The travel retail business side of WH Smith - which operates from airports, train stations and hospitals - now accounts for more than 85% of its profit and operates 1,200 stores across 32 countries.
The Post Office said it had been in contact with WH Smith to "understand more about their plans for their High Street stores".
A CWU spokesperson said any potential closures would be "devastating, but they are sadly all too predictable".
"For far too long, certain communities are being turned into postal deserts, and bad economic decisions are eroding High Streets up and down the country," the union said.