(NewsNation) — Republican attorneys general in 24 states are warning major credit companies not to move forward with plans to categorize sales made at firearms retailers.

Payment processors Visa, Mastercard and American Express have all said they plan to add merchandise codes for gun shops, a major win for gun control advocates who say it will help better track suspicious surges of gun sales that could be a prelude to a mass shooting.

The effort against the plan is being led by Tennessee Attorney General Jonathan Skrmetti and Montana Attorney General Austin Knudsen, who said in a letter to the companies the plan won’t protect consumers, the Wall Street Journal reported.

“This should be concerning to every citizen,” Knudsen said Monday on “On Balance With Leland Vittert.” “What’s next here?”

Credit card companies use merchant category codes to identify retailers by the goods and services they sell. Gun retailers are currently coded under broader categories such as miscellaneous retail or sporting goods stores.

Gun advocates and some Democratic lawmakers have hailed plans by banks and payment processors to flag purchases as suspicious, arguing it could help prevent mass shootings. The Uvalde, Texas, shooter purchased his weapon with a bank card, and the Pulse Nightclub attacker put more than $26,000 in guns on a credit card a week beforehand.

Even so, Knudsen said there’s too much ambiguity and subjectivity.

“What constitutes suspicious?” Knudsen said. “If I buy a gun safe, I’m trying to secure my firearms, that can be a large purchase.”

Merchant codes already exist for hundreds of types of stores, and in a statement last week Visa said they aren’t intended to track any sort of sales and wouldn’t prevent any gun purchases. Payment companies can’t see what a shopper buys, just the type of store in which they bought it.

“We do not believe private companies should serve as moral arbiters,” the company said. “Asking private companies to decide what legal products or services can or cannot be bought and from what store sets a dangerous precedent.”

The payment industry has long been divided on the specific categorization of gun sales, with some executives raising concern it could lead to more codes for cracking down on businesses such as abortion providers.

Knudsen said he would “absolutely” be against merchant codes for the purchase of abortion pills. If there’s a desire to flag certain types of merchandise, Knudsen argued it should be done by Congress via legislation.

Shoppers could also just use cash, too.

“Purchasers are smart,” Knudsen said.