Forty-eight Republican senators signed a letter to Attorney General Merrick Garland on Thursday slamming the Biden Administration’s plan to ban most pistol braces.

The senators blasted an ATF proposal to reclassify guns equipped with the braces as short-barrel rifles and subject them to the National Firearms Act (NFA). They warned the reclassification would mean owners who don’t register their guns would face felony charges and up to 10 years in federal prison per gun.

“The way the proposed rule is written makes clear that ATF intends to bring the most common uses of the most widely possessed stabilizing braces within the purview of the NFA,” the senators said in the letter. “Doing so would turn millions of law-abiding Americans into criminals overnight, and would constitute the largest executive branch-imposed gun registration and confiscation scheme in American history.”

The letter comes as negative public comments have flooded in on the proposal. Americans have already submitted over 100,000 comments and dozens of the comments reviewed by The Reload showed universal opposition to the proposal. If the proposal receives enough opposition, it could be pulled like other rule-change proposals in the past, including a similar pistol brace ban proposed last year and an Obama Administration attempt to ban a type of ammunition commonly used in AR-15s.

However, President Joe Biden doubled down on the brace ban Wednesday in his newly announced strategy to combat the rise in violent crime. The ATF cited just two crimes committed with braced pistols—mass shootings in Ohio and Colorado—in the proposal but did not explain whether the brace contributed to those crimes. The Republican senators said the proposal would do nothing to reduce the recent murder spike.

“A crime wave is sweeping America,” they said. “These aren’t broken-windows crimes; they are violent crimes like murder, assault, and robbery. But rather than cracking down on the criminals who are turning America’s cities into warzones, ATF and the Department of Justice have decided to go after law-abiding gun owners who are minding their own business and using equipment that ATF seemingly blessed in 2017.”

The White House did not respond to a request for comment. April Langwell, chief of the ATF’s Public Affairs Division, said the agency “cannot comment on the proposed rulemaking, nor on the communications between the agency and Congress” and DOJ spokesperson Kristina Mastropasqua confirmed the department received the letter but offered no further comment. Gun-rights advocates cheered the letter with Firearms Regulatory Accountability Coalition president Travis R. Stevens-White, who represents pistol brace manufacturers, thanking Senate Minority Leader Mitch McConnell (R., Ky.) for “taking point and assisting our efforts in aggressively defending manufacturers from government overreach.”

Rob Portman of Ohio and Susan Collins of Maine were the only Republican senators not to sign the letter. Their offices did not respond to a request for comment.

The other 48 Republican senators said the ATF made the devices popular by initially approving their design and then expanding their legal use in a 2017 determination. They accused the agency “suddenly chang[ing] course” on their legality after nearly a decade. They said the ATF’s turnabout was “shocking,” and accused it of trying to “yank the rug out from under” law-abiding American gun owners who have purchased upwards of 7 million of the devices.

“Demand over the last five years is surely attributable to ATF’s classification letters and much publicized effective [sic] 2017 letter effectively rescinding its 2015 ruling against stabilizing braces,” the senators said. “Demand for stabilizing braces therefore should not be attributed to the lawlessness of gun owners, but rather to their desire to exercise their Second Amendment rights consistent with how ATF interpreted the law in 2017.”

The senators also pointed out several practical issues with enforcing the proposal as the ATF laid it out.

“Missing from ATF’s reasoning, of course, is that, even in its own very conservative estimate, ATF requires many months to process the registration forms for [short-barrel rifles],” they said. “Thus, gun owners will have to give up the use of their firearms for months while waiting for ATF to process their registration forms and tax payments.”

They said the ATF doesn’t have a viable way for Americans to determine whether their braced pistol requires registration under the rule.

“Does ATF expect individuals to apply the proposed rule’s vague and confusing criteria on their own, knowing that a good-faith error could land them in prison?” they said. “If not, are gun owners expected to ship off their firearms at their own expense to ATF’s Firearms and Ammunition Technology Division (FATD) for classification? We understand that FATD currently takes about a year to classify a single firearm under its current workload. Does ATF actually expect millions of gun owners to ship off their firearms to FATD potentially for years while awaiting a classification decision?”

Ultimately, the senators accused the ATF of purposely attacking gun owners.

“The proposed rule is worse than merely abdicating your responsibility to protect Americans from criminals; you’re threatening to turn law-abiding Americans into criminals by imposing the largest executive branch-initiated gun registration and confiscation program in American history,” the senators said. “We urge you to turn back. Correct this mistake and withdraw the proposed rule.”