A U.S. senator this week criticized the gun industry for secretly harvesting personal information from firearm owners for political purposes, calling it an “invasive and dangerous intrusion” of privacy and safety.

In a letter sent to the National Shooting Sports Foundation on Tuesday, Sen. Richard Blumenthal, D-Conn., questioned the legality of the “covert program” in which firearms manufacturers for years shared sensitive customer information with political operatives.

Blumenthal cited a ProPublica investigation that found some of America’s most iconic gunmakers secretly participated, even while the gun industry presented itself as a privacy protector and fought against government and corporate efforts to track firearms ownership.

At least 10 gun industry businesses, including Glock, Smith & Wesson and Remington, handed over hundreds of thousands of names, addresses and other private data — without customer knowledge or consent — to the NSSF, which then entered the details into what would become a massive database. The database was used to rally gun owners’ electoral support for the industry’s candidates running for the White House and Congress.

Blumenthal, who chairs a Senate subcommittees on privacy, gave the NSSF a Nov. 21 deadline to answer several questions. He wanted to know more about which companies contributed information to the database, the type of customer details shared and whether the data is still being used by the organization or by others.

The senator, who served as Connecticut’s attorney general for two decades and has consistently supported legislation to reduce gun violence, said he was also “disturbed” by “glaring discrepancies” between what ProPublica uncovered and the NSSF’s previous responses to his office.

In 2022, Blumenthal sent the NSSF a list of questions after reading leaked documents that made a passing reference to the database. In its response, the NSSF would not acknowledge the database’s existence.

“The secretive compilation and sharing of private information by NSSF and its partners seems to have violated federal consumer protection laws and created substantial data privacy and safety risks for lawful gun owners,” Blumenthal wrote.

The customer information initially came from decades of warranty cards filled out and returned to gun manufacturers for rebates and repair or replacement programs. A ProPublica review of dozens of warranty cards from the 1970s through today found that some promised customers their information would be kept strictly confidential. Others said some information could be shared with third parties for marketing and sales. None of the cards informed buyers their details would be used by lobbyists and consultants to win elections.

Violating a promise of strict confidentiality on warranty cards or failing to mention that consumer information could be given to the NSSF may qualify as a deceptive practice under the Federal Trade Commission Act, privacy and legal experts said. Under the law, companies must follow their privacy policies and be clear with consumers about how they will use their information.

The NSSF did not respond to messages seeking comment. Previously, the group defended the data collection, saying in a statement to ProPublica that any suggestion of “unethical or illegal behavior is entirely unfounded.” The statement said “these activities are, and always have been, entirely legal and within the terms and conditions of any individual manufacturer, company, data broker, or other entity.”

Glock and Smith & Wesson did not previously respond to ProPublica’s requests for comment. In the years since the data sharing program was launched, Remington has been split into two companies and sold. Remarms, which owns the old firearms division, said it was unaware of the company’s workings at the time. The other portion of the company is now owned by Remington Ammunition, which said it had “not provided personal information to the NSSF or any of its vendors.”

Founded in 1961 and currently based in Shelton, Connecticut, the NSSF represents thousands of firearms and ammunition manufacturers, distributors, retailers, publishers and shooting ranges. While not as well known as the chief lobbyist for gun owners, the National Rifle Association, the NSSF is respected and influential in business, political and gun-rights communities.

For two decades, the organization has raged against government and corporate attempts to amass information on gun buyers. As recently as this year, the NSSF pushed for laws that would prohibit credit card companies from creating special codes for firearms dealers, claiming the codes could be used to create a registry of gun purchasers.

As a group, gun owners are fiercely protective about their personal information. Many have good reasons. Their ranks include police officers, judges, domestic violence victims and others who have faced serious threats of harm.

The gun industry launched the data harvesting approximately 17 months before the 2000 election as it grappled with a cascade of financial, legal and political threats.

Within three years, the NSSF’s database — filled with warranty card information and supplemented with names from voter rolls and hunting licenses — contained at least 5.5 million people. The information was central to what NSSF called its voter education program, which involved sending letters, postcards and later emails to persuade gun buyers to vote for the firearms industry’s preferred political candidates.

Because privacy laws shield the names of firearm purchasers from public view, the data NSSF obtained gave it a unique ability to identify and contact large numbers of gun owners or shooting sports enthusiasts. The NSSF has credited its program for helping elect both George W. Bush and Donald Trump to the White House.

In April 2016, a contractor on NSSF’s voter education project delivered a large cache of data to Cambridge Analytica, a political consulting firm credited with playing a key role in Trump’s narrow victory that year, according to internal Cambridge emails and documents. The company later went out of business amid a global scandal over its handling of confidential consumer data.

The data given to Cambridge included 20 years of gun owners’ warranty card information as well as a separate database of customers from Cabela’s, a sporting goods retailer with approximately 70 stores in the U.S. and Canada.

Cambridge combined the NSSF data with a wide array of sensitive particulars obtained from commercial data brokers. It included people’s income, their debts, their religion, where they filled prescriptions, their children’s ages and purchases they made for their kids. For women, it revealed intimate elements such as whether the underwear and other clothes they purchased were plus size or petite.

The information was used to create psychological profiles of gun owners and assign scores to behavioral traits, such as neuroticism and agreeableness. With the NSSF supporting Trump and pro-gun congressional candidates, the profiles helped Cambridge tailor the NSSF’s political messages to voters based on their personalities.