If you process online payments by credit or debit card, you fall under PCI DSS (Payment Card Industry Data Security Standard). This standard was drawn up by the major payment networks (Visa, Mastercard, American Express) and applies to every company that processes, stores or transmits payment card data.
PCI DSS is not a law but a contractual obligation. Your payment provider or acquirer requires compliance. If you do not comply and a breach occurs, your ability to take payments can be suspended and considerable fines imposed. Version 4.0 of the standard, fully in force since 2024, sets higher requirements than its predecessor.