Lloyds Bank is facing fresh anger over the closure of a further 100 branches, resulting in more than 200 job losses.
Unite said the "continuous stream" of branch closures by the UK's retail banks appeared to show no signs of ending.
The union said the announcement will affect 54 Lloyds branches, 22 Halifax branches and 24 Bank of Scotland branches.
Rob MacGregor, Unite national officer, said: "The loss of a further 100 local banks will be painful for high streets across the country to absorb.
"Unite is angered that another 200 staff have today been told that their job will be cut due to their branch shutting.
"Lloyds Banking Group's rationale for branch closures is the claimed customer preference towards the use of technology across banking.
"However this simply doesn't ring true when it's clear that many customers still value the face to face engagement with experienced and knowledgeable bank staff.
"The industry must halt these endless branch closure programs and open their eyes to what these closures are doing to rural communities, their disabled customers and the small business customers who depend on access to a local branch."
A Lloyds spokesman said the group's retail division was cutting 325 jobs as part of previously announced reductions under a management restructuring, while 96 new roles will be created.
The 100 branches will close between July and October, part of some 200 closures announced last summer.
"These branch closures - previously announced in July 2016 - are in response to changing customer behaviour, and the reduced number of transactions being made in branches," said the spokesman.
"Our branches will continue to play a vital role in our multi-channel approach to meeting the full range of customer needs, and we expect to continue to have the biggest branch network in the UK.
"As we continue to make investment in our network, we will further expand the mobile branch fleet across Bank of Scotland and Lloyds Bank, with the addition of nine new mobile branches. This will provide continuity of services in some of those areas affected by branch closures, alongside other ways to access banking locally.
"We are committed to working through the changes announced today in a careful and sensitive way. All affected employees have been briefed this morning, and our recognised unions were consulted in advance and will continue to be consulted throughout the process.
"The group's policy is always to use natural turnover and to redeploy employees wherever possible. Where it is necessary for employees to leave the company, wherever possible, this is achieved through offering voluntary redundancy. Compulsory redundancies will always be a last resort."