Laws taking effect Monday in California and Tennessee highlight the nation’s stark divide over guns: While the former is looking to help banks track potentially suspicious gun purchases in hopes of thwarting mass shootings and other firearm-related homicides, the latter is seeking to prohibit the practice. 

Major credit card companies as of today have to make a merchant code available for firearm and ammunition retailers to comply with California’s new law to aid banks in monitoring gun sales and flag suspicious cases to authorities. The law requires retailers that primarily sell firearms to adopt the code by May 2025.  

Democratic-led legislatures in Colorado and New York this year also passed measures mandating firearms codes that kick in next year. 

The idea behind a gun merchant code is to detect suspicious activity, such as a person with no history of buying firearms suddenly spending large sums at multiple gun stores in a short period of time. After being notified by banks, law enforcement authorities could investigate and possibly prevent a mass shooting, gun control advocates contend.

On the other side of the issue, gun-rights advocates are concerned the retail code could impose unfair scrutiny on law-abiding gun purchasers. During the past 16 months, 17 states with Republican-controlled legislatures have passed bills banning a firearms store code or curtailing its use. 

“We view this as a first step by gun-control supporters to restrict the lawful commerce in firearms,” Lawrence Keane, senior vice president of the National Shooting Sports Foundation, told the Associated Press. 

California’s measure coincides with a separate state law in Tennessee that bans the use of firearm-specific merchant codes, with the National Rifle Association lauding it as protecting the financial privacy of gun owners. 

Mastercard, Visa and American Express worked to comply with the new California measure, as CBS News reported earlier in the year. The credit card networks had initially agreed to implement a standalone code for firearm sellers, but put that effort on hold after objections from gun-rights advocates. 

Credit cards are used to facilitate gun crimes all across America, according to Guns Down America, which argues at retail codes could prevent violence stemming from cases of straw purchases, gun trafficking and mass casualty events. 

A report by the nonprofit advocacy cited eight mass shootings that possibly could have been prevented, including the Aurora, Colorado, movie theater shooting and the Pulse Nightclub shooting in Orlando, Florida, because each perpetrator used credit cards to mass arsenals in a short period of time. 

U.S. Surgeon General Vivek Murthy last week decried gun violence to be an escalating public health crisis, with more than 48,000 Americans killed with firearms in 2022.

—The Associated Press contributed to this report.