Credit card companies have long categorized your spending using merchant category codes, or MCCs. They are four-digit numbers that networks use to identify types of merchants by the goods and services they sell. They label purchases such as shopping, gas, fast food, etc. Now, a new MCC to separate and distinguish gun purchases has been approved by the International Organization of Standardization.

Gun retailers were previously labeled as general retail.  American Express, Mastercard, and most recently Visa have agreed to implement the new system while still supporting lawful purchases and protecting consumer privacy.

“Following ISO’s decision to establish a new merchant category code, Visa will proceed with next steps, while ensuring we protect all legal commerce on the Visa network in accordance with our long-standing rules,” Visa said in a statement.

Gun-control advocates recently stepped up their long-running campaign to get banks and credit card companies to do more to track and flag suspicious firearms sales. Earlier this month, Democratic lawmakers wrote to Visa, Mastercard and Amex pushing for the implementation of a new MCC for gun and ammunition sellers, citing recent examples of credit cards being used to buy guns that were later used in mass shootings.

Some previous mass shooters have lengthy receipts of gun purchases. The man who killed 49 people at Pulse Nightclub bought $26,000 worth of guns and ammo on credit cards. The Las Vegas Musical Festival shooter charged $95,000 on dozens of guns. The shooter who terrorized a Colorado movie theater charged more than $9,000 worth of guns and tactical gear in the two months before his attack.

Gun rights advocates and gun lobbyists have said categorizing gun shop sales would be unfair to the industry given that most firearm sales do not result in mass shootings. The National Rifle Association released a statement against the credit card companies’ decision to implement the new gun code.

“The [industry’s] decision to create a firearm-specific code is nothing more than a capitulation to anti-gun politicians and activists bent on eroding the rights of law-abiding Americans one transaction at a time,” National Rifle Association spokesman Lars Dalseide said.

The approval of the new tracking system comes with a complicated history. ISO had denied such a request to implement a gun code twice before and the three major credit card companies were against it. Visa had expressed concerns about the proposal in its early stages. In a statement, Visa said “we believe that asking payment networks to serve as a moral authority by deciding which legal goods can or cannot be purchased sets a dangerous precedent.”