The Blackfriars Road post office will shut down later this month after its operator said it intended to stop the service.
Post Office bosses have said the closure of the branch near Waterloo East Railway is temporary.
Private operator ZCO Ltd took over the branch in 2018 when it was being run directly by Post Office Ltd.
“We are writing to inform you that, regrettably, following the resignation of our retail partner ZCO Ltd and the withdrawal of the premises for Post Office use, the above branch will be closing temporarily on Tuesday 31 January 2023 at 17:30,” wrote Sarah Wileman of Post Office Ltd.
“I would like to assure you that we are working hard to keep any period of closure to a minimum and we are currently investigating the options available which will enable us to reinstate a Post Office service to the local community.
“In exploring this, it is important that any future service is sustainable for the person operating the service, and for Post Office Limited.”
Customers are being told to use post offices at the corner of Cornwall Road and Upper Ground and at the Co-op on Southwark Bridge Road.
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Last month, it was announced that a local family had opened a brand new post office in Bermondsey, restoring much-needed services to the local area.
Postmaster Faheem Sheikh, a former Ark Globe Academy student, swung the doors open on Friday, December 16.
Based inside the new Bagh Convenience Store, next to the Spit and Sawdust pub, the post office replaces the Great Dover Street branch which closed in 2018.