A coalition of congressional Democrats on Thursday called on President Biden to reverse a Trump-era change to the regulation of 3D-printed ghost guns and return oversight to the State Department as munitions.

“[I]t is far too easy for anyone to download from the internet the computer code to 3D-print unserialized, untraceable, plastic ‘ghost guns,’” the group, which includes Democratic Sens. Sheldon Whitehouse (R.I.), Cory Booker (N.J.), Richard Blumenthal (Conn.) and Elizabeth Warren (Mass.), said in a letter to Biden, first obtained by Politico. “These 3D-printed weapons circumvent our system of gun safety rules and regulations, and pose a serious threat to public safety and national security.”

3D-printed ghost guns and their technical data were previously regulated by the State Department on its Munitions List. However, President Trump approved their removal from the weapons list in January 2020 and moved regulation to the Commerce Department.

The group of House and Senate Democrats criticized the Trump-era change in Thursday’s letter, noting that its narrow guidance only applied to software and technology posted online that is “ready for insertion” into a 3D printer.

Because the guidance is so narrow, the group warned that people could easily evade it by advertising files for 3D-printed guns online but sending the actual software via email. They also noted that it doesn’t cover files that can easily be converted into a format for 3D printing.

The group, which also included Rep. Ro Khanna (Calif.) and Del. Eleanor Holmes Norton (D.C.), urged the return of 3D-printed ghost guns to State Department regulation, where they would be subject to pre-approval before being placed in the “public domain.” If oversight remains in the Commerce Department, they asked that Biden “at a minimum” strengthen the current guidelines to close the existing loopholes.

The Biden administration has previously made efforts to crack down on the proliferation of ghost guns. A new rule from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), which went into effect in August, subjected ghost guns to the same rules as traditional firearms, including requiring background checks and serial numbers.