HARRISBURG, Pa. (AP) — Pennsylvania 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 police 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% receivers, also known as unassembled “ghost guns.”

Democratic Attorney General Josh Shapiro last month issued a legal opinion that the 80% 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.

Joshua Prince, a lawyer representing businesses that manufacture gun frames for sale that have sued to challenge the policy, said the latest guidance from state police does not make it clear what qualifies as a partially manufactured frame or receiver. That is a particular problem because there are potential criminal penalties for violations, he said.

“No one knows what it does or does not refer to,” Prince said. “How many hardware stores are now in violation of the law for selling a piece of metal?”

Prince used as an example an online recap by someone who made an AK-47 using parts from a rusty shovel.

Shapiro advised state police to treat unassembled gun frames as firearms if they are designed to expel a projectile by the action of an explosive, or if they can be readily converted to do so.

“No single factor is dispositive,” Shapiro said, adding that “all the applicable factors” needed to be considered to determine if the part or parts can be readily converted into working guns.

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