A target of 10,000 signatures has been set to help save Eastbourne's main post office.
Campaigners have until October 16 to put forward their views to Post Office Ltd managers about the controversial closure proposals.
The town centre Upperton Road branch is one of five earmarked to go. Others are in Avard Crescent, Church Street and Compton Street, while a decision has already been made to close a branch in Whitley Road.
More than 4,200 signatures have already been put on one petition organised by Eastbourne's Liberal Democrat group.
Protesters yesterday presented it to Upperton Road branch manager Cliff Ward.
Stephen Lloyd, Lib Dem parliamentary spokesman, said: "If we can gather 10,000 signatures by October 16, the Post Office will have to listen. The sheer number of people who have backed the campaign in the last few weeks sends an impressive signal.
"Hitting 10,000 signatures will mean the Post Office will have to recognise what an appalling blow closing Upperton Road would be."
The closure plans have provoked cross-party condemnation. Up to 60 per cent of small companies questioned by the Federation of Small Businesses (FSB) believe their businesses will collapse if the closures go ahead.
A delegation led by Eastbourne Tory MP Nigel Waterson travelled to London on Monday to confront post office managers.
They managed to gain concessions from Post Office Ltd, including an extension to the consultation deadline and a promise they will face branch users at a public meeting.
A Post Office Ltd statement said: "Even after any changes, well over 95 per cent of customers will still live within a mile of a post office branch.
"We have made sure the Old Town branch, Green Street branch, the Terminus Road branch and the Meads branch would be geared up to cope with extra customers."
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 The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.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 hereComments are closed on this article