TSB has revealed most of its Scottish branches will only open for two or three days a week from July.
The changes will apply to 71 sites in Scotland and 22 in England.
In addition, four Scottish branches are being closed – in Edinburgh, at Haymarket and Fountainbridge, Aberdeen’s Holburn Street branch, and another in Keith, Moray.
TSB has said there will be no job losses as a result of the shake-up this summer.
The bank has set out figures showing the fall in branch visits by customers, while there has been a sharp increase in the use of online and phone banking, and visits to alternative branches.
The Glasgow Anniesland branch, for instance, has seen a recent drop in footfall of 19%, while there has been a 90% boost in the use of alternative forms of banking.
The Federation of Small Businesses in Scotland said the cut in hours looked like a prelude to further closures.
Andrew McRae, the trade body’s policy chairman, said: “In scores of communities these changes will reduce local footfall, hurting the vibrancy of many of our high streets. It will make it more difficult to run a business, especially if you operate in our cash-dependent retail and hospitality industries.
“UK ministers must stop sitting on their hands when it comes to bank branch closures and uncertainty over our cash machine network. We need to see policy-makers look at the impact of these sort of closures on the economic health of local communities.”
In a statement on its website, TSB said it “remains committed to having a strong branch network”, adding “there will also be no job losses as a result of these changes, with all partners in the closing branches being offered roles in other nearby branches”.