Vermont Gov. Phil Scott, a Republican, has allowed a bill to become law that requires serial numbers on firearms that are privately made with individual parts, kits or 3D printers.

Scott allowed the bill, part of an effort to crack down on hard-to-trace ghost guns that are increasingly showing up in crimes, to become law without his signature. He said in a letter to lawmakers Tuesday that while he agrees that firearms should be serialized as a public safety measure, he has concerns about the law’s “practicality and impact.”

“Over the last decade, as anti-policing policies increased and criminal accountability has steadily decreased, violent crime has grown in Vermont,” Scott wrote. “This is why I believe we should instead focus on measures that will reverse these trends over those, like S.209, that are unlikely to have any measurable impact on violent crime.”