Handguns could be mailed through the U.S. Postal Service for the first time in nearly 100 years if a proposed rule under the Trump administration takes effect, the Postal Service said as it weighs public comments on the change.

The policy debate centers on whether the Postal Service can allow shipments of concealable firearms such as pistols and revolvers. The U.S. Postal Service has previously allowed some firearms to be mailed—such as long-barreled rifles and shotguns—under conditions including that the guns be unloaded and securely packaged, but it has treated handguns differently under longstanding restrictions.

In its review of the legal framework, the U.S. Department of Justice revisited a 1927 law that barred USPS from mailing concealable firearms unless they came from licensed dealers. The DOJ said that law is unconstitutional and that it conflicts with the Second Amendment, arguing that the postal service cannot refuse to ship constitutionally protected firearms to and from law-abiding citizens even if the mailer is not a licensed manufacturer or dealer.

The Postal Service said it is reviewing public comments that were due Monday before making final changes. Under the proposal described by the Postal Service, people would be able to sell and ship a handgun to a recipient within state lines, according to the Democratic attorneys general who opposed the rule.

The attorneys general also said the rules would be tighter for mailing across state lines, describing a requirement that people could only mail to themselves in the care of another person and would have to open the package themselves. They argued that these limits are designed to help people traveling to another state who want a firearm for recreation, but they said the proposal would still bypass state oversight systems.

Nevada Attorney General Aaron Ford, a Democrat running for governor, said the change would “undo the work states like Nevada have done to curb gun violence” following the Oct. 1, 2017 Las Vegas mass shooting, which he cited as resulting in 60 deaths. Ford said the proposal would make it easier for “criminals and abusers” to access firearms, and he described it as a “slap in the face” to gun violence survivors and law enforcement.

Ford and other attorneys general said states impose requirements through state entities, including firearms safety courses, background searches and checks related to mental health history. They argued that the proposed USPS change would allow shipments that could avoid those state requirements and make it harder to guarantee compliance, and they warned that law enforcement would need to create a new firearms tracking structure—adding burdens to state budgets.

Private carriers also have their own limits on gun shipments, the report said. Companies including UPS and FedEx restrict shipments of firearms to customers with federal firearms licenses, such as importers, manufacturers, dealers and collectors, according to the companies’ published guidance, including FedEx requirements for approval.

Gun rights advocates and gun safety organizations responded differently to the proposal. John Commerford, executive director of the lobbying arm of the National Rifle Association of America, called it a “key victory for law-abiding gun owners” and said USPS would allow handguns to be shipped under the same “commonsense safety conditions” already applied to rifles and shotguns.

John Feinblatt, president of Everytown for Gun Safety, said the rule change would turn USPS into a “gun trafficking pipeline” for illegal weapons, while he warned it would strip law enforcement of tools needed to prevent and investigate gun crime.