Taxpayer-backed Royal Bank of Scotland is closing 44 branches across the UK - including 14 classed as "last banks in town", with seven in Scotland.
The bailed-out lender said the move comes after a 30% drop in branch transactions since 2010.
RBS, which is just over 80% owned by the Government, said the so-called last banks in town that are closing are generally only open for a few hours a week and see one or two customers an hour.
But campaigners said the group was letting customers down.
The last banks in town in Scotland that closed are Bonnybridge, Castletown, Chirnside, East Linton, Greenlaw, Longniddry and Pathhead.
A spokesman for RBS said: "Banking has changed significantly over the last few years as more and more of our customers are banking with us where and when it is convenient for them."
He added: "We have to adapt to what our customers want, which is why we're investing in a range of other ways our customers can bank with us, including online and telephone banking, our mobile app, and in any one of the Post Office's 11,500 branches across the UK."
RBS said it had been telling affected customers about the closures over the past two months.
Campaign group Move Your Money said RBS had "consistently undermined the interests of its customers and wider society since being bailed out in 2008".
The group's campaign director Charlotte Webster added: "It's no surprise then to see the bank let down its customers once again by upping sticks and leaving town - even where it's promised not to do so.
"Banks of this scale just can't be trusted to take its customers' needs into account, even when the only reason it's still around is because of our support."
The branch closures come after RBS said in February it planned to slash costs by more than £5 billion over the next three to four years after slumping into the red by £8.2 billion in 2013.
It has around 2,000 branches across the UK, although it is spinning 314 of those off into its Williams & Glyn brand to meet European Union rules on state aid.
The group announced in February that customers of RBS as well as its sister banks NatWest and Ulster Bank would be able to use any of the Post Office's 11,500 branches to pay cheques or cash into their accounts from later this year.
RBS already has a relationship with the Post Office which enables its customers to withdraw cash and check their balances at Post Office branches.
The branches are being shut throughout May and June.
RBS said it was too early to give details on redundancies as it hopes to redeploy staff at other branches where possible.
Some employees will also transfer to mobile banking services being launched in certain areas where branches are closing.
The latest closures follow 60 branches that were shut last year and RBS refused to rule out further closures.
Trade union Unite accused RBS of "turning its back on local communities" and urged the Government to intervene.
Rob Macgregor, Unite national officer, said: "Taxpayers have a right to be angry that RBS has quietly embarked on a major programme of branch closures.
"While RBS senior executives get millions of pounds in payouts, there are communities up and down the country being denied access to a local bank."
He added that Chancellor George Osborne should take action as one of the branches closing is in his constituency of Tatton in Chelford.
The Campaign for Community Banking Services (CCBS) said the decision by RBS sees it break a pledge made in 2010 to safeguard "last bank in town" branches.
RBS had since watered down its commitment, with each case considered on its own merits.
Derek French, director of the CCBS, said: "It is time for action not words and I call upon Government to intervene now and order the banks to fully consider the branch-sharing alternative before leaving communities without a staffed bank presence."