One of them, Metro Bank, overcharged 92 people for unarranged overdrafts.
The Competition and Markets Authority has also ordered changes at Barclays, HSBC, Lloyds Banking Group, NatWest, along with the Bank of Ireland. The CMA identified breaches from showing the correct interest rates through to accurately displaying locations and opening times.
The watchdog said it was “disappointing that these six banks have failed to uphold rules that have been in place for the last five years”.
All six are to make changes to prevent further breaches.