The Royal Bank of Scotland, which is 82% owned by the taxpayer, is to cut over 600 jobs from its financial planning service, bringing its total staff reductions to 36,000 since 2008.
Unite has branded the move as "brutal" as the cuts represent a 50% reduction in the department across the country.
National officer David Fleming said: "These latest Royal Bank of Scotland job losses are brutal.
"Unite, for some time, has had major concerns about the appalling manner in which these workers at the bank have been treated.
"Those losing their jobs today are a highly-skilled workforce, and the bank has refused to take into account economic factors which have impacted performance and achievability of targets."
But RBS, which has cut more than 35,000 jobs since Chief Executive Stephen Hester was brought in to turn the bank around when it was bailed out in 2008, defended the move.
They said the jobs would go as a result of new UK rules requiring retail financial products such as savings and investment vehicles to be sold by more highly qualified staff and charged a fee.
An RBS spokesman, said: "As a response to this we will be reducing the number of roles by 618 across the UK and creating 351 new roles."
He added: "Having to cut jobs is the most difficult part of our work to rebuild RBS and repay taxpayers for their support.
"We continue to make efficiencies across our business to deliver greater value to our customers and shareholders."
Earlier this year, RBS was under fire for paying out just under £800m in bonuses to its employees for their work in 2011.