What are used by the bank system to restrict cardholders from buying certain products or services?

Banks use various mechanisms to restrict cardholders from purchasing certain products or services, including transaction monitoring systems that analyze spending patterns and flag suspicious activity. They may implement merchant category codes (MCC) to categorize transactions, allowing them to block purchases from specific industries, such as gambling or adult entertainment. Additionally, banks may set individual spending limits or restrictions based on a cardholder's account status or risk profile.