Lloyds Bank is to axe 625 jobs and offshore work to India, according to union officials.
Unite said the cuts will affect several of the bank's divisions, including consumer finance, commercial banking and legal, hitting offices in London, Brighton, Gloucester, Leeds, Halifax and Wolverhampton.
The cuts are part of 9,000 job losses announced by the bank in 2014, said Unite.
Around IT 80 jobs will be moved to India, according to the union.
Unite regional officer John Morgan-Evans said: "It is alarming that Lloyds are continuing to offshore IT roles in the name of driving down cost. This simply means that the bank want to pay an IT worker in India less for the same work carried out in the UK. This disastrous race to the bottom hurts our members and inevitably impacts customers.
"Unite has made it clear that 'efficiency' cannot simply mean axing more jobs while expecting the same work to fall on fewer shoulders.
"The bank forgets that these relentless cuts have a human cost. Unpaid overtime and work-related stress are already at endemic levels across the bank and this will reach a crisis point if Lloyds continue to swing the axe."
Unite said the job losses will be followed by a recruitment freeze in several of the bank's divisions, while many staff will have to go through a new assessment process, increasing worries of further cuts.
The cuts are taking a heavy toll on workers, with three out of four reporting symptoms of stress, while four out of five are working unpaid overtime every week, the union claimed.