There are calls for greater action as more than 50 banks are closing every year in Wales.
Which? says closures have rapidly increased in the last four years with Brecon and Radnorshire being the hardest hit. It has lost 14 banks since 2015.
Dwfor Meirionnydd has lost 13 while Carmarthen West and South Pembrokeshire saw 12 branches shut in the same period.
The number of cashpoints that have closed between December 2017 and March 2018.
were unable to use their debit or credit card in the last year due to a technical failures.
NatWest has shut the most branches (70) in Wales between 2015 and 2018. This is followed by HSBC who closed 46 branches in this same period, then Barclays (41) and Lloyds (27).
Which? will give evidence to the National Assembly’s Economy, Infrastructure and Skills Committee for its Access to Banking inquiry.
It says It says millions of people risk being left behind without urgent action.
Welsh communities are being hit by a double whammy of soaring bank branch closures and cash machines vanishing at an alarming rate - leaving many people at risk of being stripped of cash access.
Previous research showed older generations and low-income households rely on cash the most, so are more likely to be impacted by changes to the cash landscape.