Morrisons, which operates the Morrisons Daily store on Castle Drive in Dinas Powys, which also hosts a Post Office franchise, plans to close the store in early October.
Residents and Councillors have shown their disappointment in the news, with many turning to local Facebook groups.
Plaid Cymru Councillors on Dinas Powys Community Council have launched a petition against the closure, with almost 1,000 signatures gathered to date over a small number of events.
Malcolm Phillips is one of the Councillors leading on the petition, calling on Morrisons to reverse the decision.
"We've got a population of nearly 9,000 here in Dinas Powys, it's mixed age groups, but an elderly population that relies on the post office for paying bills and getting money. There are lots of people who are alarmed, anxious and concerned about how they'd continue to access services."
"The nearest Post Offices to here are Sully, Barry or Penarth, that's okay if they're mobile and they have some way of getting there, but we've got a very age profiled population that simply can't do that. Although we've got good public transport links, theres lot of anxiety and concern, that they're worried about."
Morrisons Plfc confirmed to Bro Radio that a proposed closure will take place in early October, not July as has been announced locally.
A Post Office spokesperson said: “Our retail partner, Morrisons have reviewed their Morrisons Daily store operations and, subject to colleague consultation, are proposing to close their store at Murch. Consequently, the Post Office branches at this location would also need to close. We fully recognise the inconvenience this will cause our customers who rely on our banking and parcel services in particular.
“Should the decision be confirmed that the store is closing, we will then provide any closure date for the Post Office at that location. We will soon advertise the vacancy for the branch on our runapostoffice.co.uk website.”

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