Banking group TSB has said it is closing 36 branches and cutting 250 jobs across the business.
The job cuts will be in the fraud operations department of the bank, central operations and staff who work at the branches earmarked for closure.
The latest round of branch closures will start in September, and continue through to May next year.
Trade union Unite said the decision by the UK high street lender was a “grave mistake”.
“These workers perform essential work in the fraud departments and across the branch network,” Unite’s regional officer Andy Case said.
“Through extensive negotiations Unite has been able to substantially reduce the number of jobs at risk.
“However, that isn’t sufficient, the union is pressing TSB to urgently reconsider its damaging bank branch closures plan.”
Unite said it will be holding fresh negotiations with TSB about ways to further reduce job losses and to support members affected by the changes.
TSB said it had decided to close the local branches because not enough customers were using them.
About 96% of all the bank’s transactions take place outside of a branch, with the number of in-store transactions falling by 43% over the past four years.
A spokesman for TSB said: “The decision to close a branch is never taken lightly, but our customers are now doing most of their banking digitally and we need to move to a better balance of digital and face-to-face services.
“We remain committed to a national branch network and through innovation and integration with video, telephone, digital, branch and other face-to-face services TSB customers have more ways to bank with us than ever before.”
TSB will have 175 branches across the UK after the latest round of closures.
The lender said it is opening two more “Pods” in local communities, where customers can speak to an expert and get help with using mobile and online banking, and withdraw and deposit cash.
It will also be opening a pop-up service in six new locations which people can visit for face-to-face support, including making payments, getting product information and help with digital banking.
In February, TSB said it was setting aside £29 million for a programme of cost-saving initiatives.
It was working on reducing business expenses and generating more income by simplifying the business and making it more efficient.
It has already closed 10 branches over the past year.