Unite, the country's largest union which represents RBS staff, branded the bank's accelerating closure programme as "wholly negative and counterproductive" for the affected communities.
Over one in four of the 100 branches closed across the UK in the last six months were in Scotland.
Unite accused RBS of reneging on its commitment to maintain a banking service "where we are the last bank in town". It said 48 of this year's 100 closures are classified as last banks in town.
Unite's national officer for finance, Rob MacGregor, said: "RBS, which is 81 per cent owned by the taxpayer, has steadily and stealthily reneged on its commitment to provide banking services to often rural and ill-served communities.
"Nearly half of this year's 100 closures mean that these communities now don't have a bank - and surveys have shown that people like the face-to-face contact that having a physical presence in the high street provides.
"Pensioners, those who have mobility issues, and those without internet access are being particularly hard hit by these closures in their towns and rural areas. Unite is not alone in believing that banks, especially those owned by the taxpayer, have a duty to the wider community.
"We believe many of the branches that have been closed were making a profit - and their closure is aimed at just increasing profits. We call on RBS to reconsider its closure programme … it has a moral duty to maintain a presence in towns where it is the only bank.
"This is one way it can rebuild the public's battered trust in the banking system."
RBS said in April that it was closing 44 branches, with 14 of them the last bank in their town. The bailed-out lender said there had been a 30 per cent drop in branch transactions since 2010.
Banks have been promising not to pull out of local communities since the furore caused by Barclays a decade ago when it closed 171 branches on one day.
In its customer charter of 2010, RBS said it would not close any bank which was the last one in the community. Last month it emerged one in four RBS managers and deputy managers were to be made redundant at high-street branches in a fresh jobs cull.
An RBS spokeswoman said: "Banking has changed significantly over the last few years as more and more of our customers are using digital technology to bank with us where are when it is convenient for them.
"As a result, there has been a 30 per cent drop in branch transactions since 2011 whilst online and mobile transactions have grown by over 200 per cent.
"We review our branch network regularly and the decision to close a branch is made on a case-by- case basis, based on local information - for example when footfall has fallen. Closing a branch is a difficult decision and one we do not take lightly.
"Whenever we close a branch, we always look at other ways our customers can access similar banking services such as ATMs, mobile branches or at any of the 11,500 Post Offices across the UK."