RBS' decision is a result of changes to the pension system, which effectively increased the rate of both employee and employer national insurance applicable to DB pension systems.
The changes have led to RBS' employer national insurance bill rising by £18m, but, rather than scrape the costs from its own bottom line, the bank is passing them onto its employees.
Unite is arguing that the move, which will see 27,000 employees who are members of the DB scheme contributing an additional one per cent of their salary to their pension from October 2016 and a further one per cent on top of that in 2017, will lead to any payrises granted to lower-paid staff being wiped out.
"This shameless move will shatter the fragile trust RBS have worked to restore since the bank’s previous regime ended in calamity," said Rob MacGregor, national officer for finance at Unite. "Once again the bank have found a new way to hand down the costs of historic mismanagement to the workforce. RBS employees, who have struggled to bring the bank back from the brink deserve better."
An RBS spokesperson said: "Reforms made to DB pensions mean that the costs of our own scheme have risen. As a result RBS is proposing to increase the cost of being a member of the scheme. The bank will be consulting on this proposal with affected staff and employee representatives."
Thanks to rising costs of running such schemes, DB pensions are fast falling out of favour with employers. Research released last year by JLT Employee Benefits discovered that just 23 of the FTSE 100 were still incurring service costs on a DB scheme that would suggest a significant number of staff were benefiting from it and that ongoing provisions had dropped by 13 per cent over the course of a year.
Last week, RBS revealed that it would be cutting almost 500 jobs from its investment banking division in a bid to reduce costs as part of its restructuring plan.
Meanwhile, last month, the bank announced that it had made a loss for the eighth year in a row.