Merchant Category Code (MCC) Blocking

Implement controls to restrict or monitor financial transactions based on Merchant Category Codes (MCCs)—a globally standardized classification system defined under ISO 18245. MCCs are four-digit codes used by card networks (e.g., Visa, MasterCard, Amex) to categorize merchants by the primary type of goods or services they provide. These codes are assigned by acquiring banks and transmitted as part of the transaction metadata every time a payment card is used.

By enforcing MCC-based restrictions, organizations can block or flag high-risk purchases based on merchant intent, even when the vendor name appears benign or spending limits are not exceeded. MCC enforcement is a widely accepted control in government and private-sector purchasing policies, and provides a scalable way to mitigate insider financial misuse.

Key Prevention Measures:

Block High-Risk MCCs

Deny transactions associated with high-risk merchant categories, such as:

• 7995 – Gambling Transactions
• 4829 – Money Transfer / Wire Services
• 5967 – Direct Marketing / Teleservices
• 6012 – Quasi-Cash Transactions (e.g., crypto platforms, money orders)

Enforce Pre-Authorization Blocking

Use payment card controls to prevent transactions at blocked MCCs from completing, rather than relying solely on post-spend reviews or reconciliation processes.

Define Role-Based MCC Profiles

Assign permitted MCCs based on a subject’s job function. For example, limit access to travel-related MCCs for field staff only, and restrict electronics purchases for non-technical roles.

Alert on Suspicious Behavior

Monitor for attempts to circumvent MCC restrictions, including:

• Repeated declined transactions at blocked MCCs
• Unusual bursts of transactions across diverse or unrelated MCCs
• Usage at misclassified vendors or ambiguous MCCs

Apply MCC Rules Across All Payment Types

Ensure enforcement covers physical corporate cards, virtual cards, and integrated expense platforms to eliminate alternative channels for misuse.

Embed in Acceptable Use Policies

Reference MCC-based restrictions directly in your AUP to ensure clear policy authority, support investigative actions, and withstand scrutiny in HR or legal contexts.

MCC blocking provides a precision-level control against subtle or distributed forms of financial misuse. It is particularly effective where insiders seek to extract or redirect funds through legitimate-looking merchants operating under general-use MCCs.