The SNP's Westminster leader Ian Blackford called on Theresa May to demand that RBS keep open 62 bank branches slated for closure across Scotland.
By closing branches and replacing some with mobile banking vans, which do not provide disability access, the Royal Bank of Scotland appears to be in breach of the UK Equality Act, Mr Blackford claimed at Prime Minister's Questions.He raised the case of one wheelchair user had described her experience of banking outside as "degrading".
The Ross, Skye and Lochaber MP asked: "Does the Prime Minister agree that RBS has a legal responsibility to offer equality of services to disabled customers and will she hold RBS to account on this issue?"
Mrs May responded that such closures were commercial decisions for the banks involved, adding: "Of course we all want to be able to see that all customers are able to access the services that they need, that is both customers who are disabled and customers who live in remote areas."
The Prime Minister said the Government had established the Access to Banking Standard that committed banks to carry out a certain number of steps before closing a branch and welcomed the Post Office reaching agreement with the banks to allow "more customers than ever before to use Post Office services".
She added: "So around 99% of personal customers are able to carry out their day-to-day banking at a Post Office as a result of that new agreement, that's the Government making sure that people are covered by the services they need."
Mr Blackford responded: "I would simply say to the Prime Minister we own RBS, it's time that you took your own responsibilities. By closing these branches and replacing some with mobile banking vans which do not provide disability access, the RBS appears to be in breach of the UK Equality Act."
Mrs May replied: "Other banks are closing branches because what they see is actually less use being made of those branches, but as he has been talking about matters financial, I'm sorry that he wasn't able to stand up and welcome the fact that today's trade figures for Scotland show that their biggest export market remains the rest of the UK."
Across Scotland, 13 communities are set to lose their only bank branch once the closures come into effect.
An RBS spokesman said: "We take our responsibilities under the Equality Act 2010 very seriously. Where a customer advises us of a disability, we take steps to ensure that reasonable adjustments can be put in place to ensure that disabled customers are able to access our banking services.
"We strive to ensure that our banking services are accessible to all customers. If any of our disabled customers have difficulty accessing the services provided by their mobile branch, we would encourage them to speak directly with a member of staff."