A US judge has ordered RBS to stop using critical trade finance software from vendor Complex Systems, according to the Financial Times.
New York district judge Katherine Forrest told the bank to cease using the BankTrade software for new trade finance transactions within 60 days and completely within a year.
The ruling comes after a six year legal wrangle which began after RBS acquired Dutch banking giant ABN Amro in 2007.
ABN Amro, through its US subsidiary LaSalle, licensed BankTrade - which is used for processing transactions such as letters of credit, loans, guarantees and fund transfers - from Complex systems.
However, ABN Amro sold LaSalle to Bank of America in a bid to scupper RBS's takeover. RBS then failed to transfer the BankTrade license yet continued to use the software.
In her ruling, Forrest says RBS could "not continue benefiting from its blatant and ongoing infringement simply because stopping that infringement will be disruptive to its business".
A hearing on damages is set for 5 June, according to the FT.