The major credit card issuers are staying relatively quiet about their decision to adopt a specialized code for gun retailers.

Mastercard and American Express did not respond to multiple requests for comment on their decision-making process. Visa pointed The Reload to a recent blog post on the company’s website but did not answer any questions. The financial companies’ tight lips come as Republicans press for answers about how they plan to use the new data.

“Of course, there is no accepted, consistent, scientific, or legitimate way to determine from this data what is and what is not a ‘suspicious’ purchase,” 100 Republican congressmen said in a letter to Visa. “A gun control advocate could view any desire to own or obtain a firearm as per se suspicious.”

They said the adoption of a specific Merchant Category Code (MCC) for gun retailers is “a transparent attempt to chill the exercise of constitutionally protected rights” and sidestep legal restrictions on “firearm registries by the government.”

The relative quiet from the financial institutions has caused concerns among gun owners about how they will use the new code to ferment. While there are hundreds of MCC codes for all sorts of industries and they don’t provide direct insight into exactly what was purchased at a retailer, advocates who pushed for the change justified it by claiming it could be used to track gun sales. They said the code could identify potential mass shooters or gun traffickers using yet-to-be-developed algorithms to report “suspicious” purchases at gun stores.

“These credit card companies must now take the next step and flag suspicious transactions on gun and ammunition sales like they do for fraud and money laundering,” New York Attorney General Letitia James (D.) tweeted late last week.

Though gun-control activists and Democrats successfully pressured the industry for change, the backlash from gun-rights activists and Republicans could stall progress towards the end goal of surveillance.

The credit card companies initially opposed the MCC change which delayed the decision. However, once the International Organization for Standardization, the international group that oversees MCCs, made the change, they quickly agreed to implement it. Since then, the comments the companies have made since their adoption of the new MCC have been broadly dismissive of using it to track gun sales.

Visa spokesperson Karmina Zafiro told The Reload the company is committed to “protecting legal commerce throughout its network” when asked about how it plans to use the MCC code.

“This is exactly how we would manage the process for any other appropriate MCC, like a bicycle shop or sporting goods store,” Seth Eisen, a Mastercard spokesperson, told The New York Times. It said reducing gun violence is the job of Congress, not financial institutions.

American Express has not elaborated on its decision to use the new MCC for gun stores.

Visa went further in casting doubt on the proposed use of the code in its blog post, though. It noted that MCC codes do not provide banks or credit card processors with detailed information on what is actually purchased at individual retailers. It suggested the kind of gun purchasing surveillance sought by gun-control advocates is not possible through MCC codes.

“When we process a transaction, we have no visibility into what items a consumer is purchasing — this is true irrespective of which MCC applies to a merchant,” the company wrote.

Visa further argued private financial companies should not be the arbiters of which products Americans are allowed to buy. Instead, it said that should be decided through lawmaking.

“Asking private companies to decide what legal products or services can or cannot be bought and from what store sets a dangerous precedent,” it said. “Further, it would be an invasion of consumers’ privacy for banks and payment networks to know each of our most personal purchasing habits. Visa is firmly against this.”

The company added that its policies require the banks who use its cards to “evaluate and process all legal transactions” and would continue to do so.

“Our network does not allow any financial institution member to deny transactions for the purchase of legal goods or services based on which MCC they fall under,” it said in the post. “Visa provides our services to everyone, everywhere, so long as they are used for legal purchases. We believe that is the appropriate standard.”

Still, when asked, Visa did not explain why it agreed to adopt the new MCC designation for gun stores if it does not plan to use it for the surveillance purpose advocates of the change championed.