HARRISBURG — State police on Thursday provided guidance to gun dealers about how to perform background checks for selling partially manufactured gun frames that can be readily converted into working firearms.

The agency told dealers they must call the background check system for now and cannot simply use the online system for sales of the so-called 80 percent receivers, also known as unassembled “ghost guns.”

Democratic Attorney General Josh Shapiro last month issued a legal opinion that the 80 percent receivers are firearms under state law, prompting the state police to develop the background checks procedure and form for sales of partially manufactured frames or receivers for pistols and rifles.