A Virginia judge ruled Tuesday that people ages 18 to 20 are exempt from a new law requiring background checks for all purchases of firearms, including private sales.

Lynchburg Circuit Judge F. Patrick Yeatts largely upheld a new Virginia state law expanding background checks to all gun purchases after gun rights groups had contended that requirement was unconstitutional. But Yeatts issued a narrow injunction blocking the law’s application for 18 to 20-year-old Virginians because the current federal background check system does not allow federally licensed firearms dealers to sell handguns to or run background checks on people under 21.

“Although the Act is facially constitutional, the Commonwealth is currently unprepared to administer it in a way that does not infringe on the right of adults under 21 to purchase a handgun, the ‘quintessential self-defense weapon,'” Yeatts wrote.

At issue was a universal background check law that went into effect July 1, stating that every firearm transaction in Virginia must include a background check. Buying or selling a firearm without obtaining a background check is a Class 1 misdemeanor. Previously, only licensed dealers were required to obtain background checks.

Three individuals, along with advocacy groups Virginia Citizens Defense League, Gun Owners of America and the Gun Owners Foundation, had filed a lawsuit late last month, seeking to prevent the law from taking effect.

Commercial handgun sales to people under age 21 are prohibited in Virginia; however, before the new law took effect, Virginia allowed people to buy handguns via private sales without criminal background checks.

Attorney General Mark Herring (D) says he will appeal Yeatts’ decision.

“Universal background check systems only work if they are truly universal, and we believe this potentially dangerous judicially created loophole is without basis in the law,” Herring wrote in a statement.

Yeatts wrote in his decision that implementing the new law is challenging because the FBI’s National Instant Criminal Background Check System rejects a handgun transfer to someone under 21 years old. He added that Virginia officials say they are working with the FBI to correct the issue. 

The law is one of a battery of new restrictions on firearms that went into effect this month; others have also come under legal attack.

In June, the Virginia Citizens Defense League, Gun Owners of America and Gun Owners Foundation joined a lawsuit by a Virginia resident and a licensed firearms dealer to challenge a law that restricts handgun purchases to one a month. That legal challenge failed.