The nine-member Montgomery County Council in Maryland voted unanimously Wednesday to approve a bill that restricts the possession, sale and transfer of so-called “ghost guns” to minors.

The term ghost gun has been used to describe firearms that can be assembled and manufactured with the help of a 3D printer. Police and legislators who’ve targeted the firearms said they’re concerned because of the lack of serial numbers and that the components — plastic — make them hard to detect.

The move passed by the Montgomery County Council also bars having ghost guns within 100 yards of a “place of public assembly,” like schools, churches or parks, and prohibits making a ghost gun with a 3D printer in the presence of a minor.

“This will give both our police department another tool in the toolbox to address issues of gun violence and do so in a way that helps keep all of our residents safe” said County Council Vice President Gabe Albornoz.

The bill passed by the council focuses on minors — the county’s ability to apply broader firearms regulations is limited.

Bills restricting ghost guns are being considered in the Maryland General Assembly.