RBS is closing 32 NatWest branches and is set to cut 600 roles, according to Unite.
The banking group is shutting offices in the North, Midlands, East and London, with closures to affect other regions in coming weeks.
The North will see 18 branches close, up to 217 role losses and 220 branches change their opening hours.
RBS will close 13 branches in the Midlands and East, with as many as 176 role losses and 94 branches tweaking their trading hours.
London and the South East will see one branch close, and more than 200 role losses.
Unite regional officer Lyn Turner says: “With job losses across the country and surviving branches on reduced hours, there’s no doubt this latest round of cuts will hurt the bank’s customers as well as our members.
“With every branch closure NatWest is slamming its doors on another community, dangerously undermining the bank’s long-term future.
”Unite will consult with our members as we hold the bank to its promise to avoid compulsory redundancies.”
On 11 March RBS confirmed it would slash its face-to-face advice services, leading to around 550 job cuts.
Unite is in talks with RBS over the proposed March job cuts.
RBS has been approached for comment.