NatWest is facing court action over allegations it allowed millions of pounds worth of cash transfers to be deposited into a customer's account without raising any fraud enquiries.
The City watchdog today said it has started criminal proceedings against the taxpayer-backed bank for failing to act on money laundering rules.
The Financial Conduct Authority (FCA) alleges that "increasingly large cash deposits" were made into a NatWest customer's account, with around £365million paid in - of which some £264million was in cash.
It claims that NatWest's systems and controls "failed to adequately monitor and scrutinise this activity", which took place between November 11 2011 and October 19 2016.
NatWest is due to appear at Westminster Magistrates' Court on April 14.
It marks the first time the FCA has launched criminal prosecution under the money laundering regulations and the first time the rules have been used to prosecute a bank.
The FCA said the money laundering rules require firms to "determine, conduct and demonstrate risk sensitive due diligence and ongoing monitoring of its relationships with its customers for the purposes of preventing money laundering".
No individuals are being charged as part of the proceedings.
The regulator first alerted NatWest Group, formerly Royal Bank of Scotland, of the investigation in July 2017.
NatWest Group, which is 62% owned by the Government after a mammoth bailout at the height of the financial crisis, said it had been co-operating with the FCA's investigation to date.
The bank said: "NatWest Group takes extremely seriously its responsibility to seek to prevent money laundering by third parties and accordingly has made significant, multi-year investments in its financial crime systems and controls."
