South Woodford post office, which has survived previous attempts of closure, is set to close in the spring.
The landlord of the property in George Lane has advised the Post Office it needs to vacate the premises as there are plans to redevelop the site.
There are eight employees affected by the branch's closure, which is expected to happen in either April or May.
They can either be asked to be redeployed elsewhere in the post office network or can opt for voluntary redundancy.
There are four alternate branches within two miles of the South Woodford post office and a public consultation on service provision will start on January 28 and run until March 11.
Clive Tickner from the Communication Workers Union (CWU) said he was "horrified" that some employees might be made redundant, particularly during the pandemic.
He called the office "an essential part of the local economy" and "a vital hub to South Woodford, particularly for the elderly and infirm".
Steve Blampied, head of the directly managed branch network, said: "We continue to look for a long-term solution and will consider all options for providing post office services in the South Woodford area.
"This could include re-opening a branch in new premises operated by a retail partner or opening several smaller branches in the area, providing customers with greater convenience and longer opening hours."
Clive said anything other than a crown post office, the large offices managed directly by Post Office Ltd, will result in a downgrading of services in South Woodford and has launched a petition to try to save it.
The branch was at risk of closure in 2018 but was saved at the last minute, thanks to the efforts of almost 2,000 people that signed a petition, with help from the CWU and MP for Chingford and Woodford Green, Iain Duncan Smith.
Mr Duncan Smith said the loss of the post office would be a "huge blow" during a difficult time for the High Street.
"I'm calling upon the Post Office to reverse this decision and to make a commitment to retaining this key service for South Woodford, served by a proper postal service. Before going any further with these plans Woodford residents have a right to be fully consulted with a full explanation as to how this service will be retained in this shopping area.”
You can access the consultation at https://www.postofficeviews.co.uk/ and enter branch code 031002 or email comments@postoffice.co.uk.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here