NatWest "forced" companies to open a fee-paying business current account in order to secure a loan, according to the Competition and Markets Authority (CMA).
The watchdog said the practice, known as 'bundling', breached its rules over a three-year period. The bank will now issue a total of £600,000 in refunds.
The CMA added that hundreds of companies were charged monthly for a business account that they "may not have wanted or needed".