One of the most politically protected categories: discounted interchange tiers, won through decades of lobbying by high-volume, thin-margin chains. Also the MCC your '5% on groceries' card actually checks.
The MCC quietly sets the interchange rate, whether the purchase earns rewards, whether it's treated as a cash advance, and how risk models see the merchant. Acquirers assign it at onboarding — and miscoding is a compliance problem, not a shortcut.
Merchant Category Codes are defined under ISO 18245, with network-specific usage on top. Around 500 exist; the ones that come up in real conversations are in our lookup tool.