Knighton residents will have to travel more than 20 miles to carrying on banking with HSBC when it closes in May.
The global banking giants have announced that the Knighton branch is one of the nine to close in Wales. Despite providing assurances that balance enquiries, withdrawals and deposit can be made at the town Post Office, based at Tuffins Supermarket, residents will have to do business with the bank online or travel 21 miles to Newtown.
"Rural areas are losing out time and time again," she said. "I will meet with HSBC to discuss the impact on their customers, and have also written to Barclays to seek a commitment to keep their branch in Knighton open."
The banking giants have put the closure down to behavioural changes of customers in recent years, claiming that there has been a 40% reduction in face-to-face banking, with customers opting to transact online, via a smartphone or telephone.
They have provided assurances that there are no plans to close further branches in 2017.
Ms Williams has described the closure, earmarked for Friday, May 19, as a major blow.
She said: ÒThe last couple of months has been more encouraging for Knighton, with the reprieve of the Leisure Centre for this year and the planned expansion of Clayton EngineeringÕs factory, but this is another blow for the town."