Barclays is to cut around 1,700 frontline roles from across its branch network in the UK throughout 2014.
The move comes a week after a Coventry call-centre closed, causing 350 job losses.
The latest job cuts are expected to affect cashiers, personal bankers, operational specialists, branch managers and assistant manager roles. The bank said the move was due to increased customer use of digital banking operations.
Commenting on the decision by Barclays, Unite national officer Dominic Hook said it was a colossal mistake for Barclays Bank to announce 1,700 job cuts across its bank branches.
"These employees deliver high levels of service that customers of the bank benefit from. Such a massive reduction will be very detrimental to the bank and will also be hugely challenging for the staff remaining," Hook said.
In response to Unite, Barclays spokesperson said the way in which their customers access their banking services is changing rapidly.
"More and more people are choosing to use smart phones and technology for everyday transactions – using branches only when they need access to expertise.
"We are responding by investing in the channels that customers are increasingly using, whilst improving customer service. This means training staff so they can provide that expert support but also reducing staffing levels in our branches where there is over capacity," the spokesperson added.
"As a result of technological changes, we will be able to provide better service for our customers with fewer staff in our branches."