During arguments Tuesday, the justices suggested they will uphold regulation that prohibits the sale of the kits as a reasonable interpretation of the 1968 law that restricts the sale of firearms.

The Supreme Court on Tuesday signaled a willingness to uphold a Biden administration regulation on “ghost guns,” mail-order kits that allow people to build untraceable weapons at home and that are turning up at crime scenes with greater frequency.

Conservative justices look split on whether the gun-kits rule goes beyond what Congress allowed. A Supreme Court argument about the government’s ability to ban so-called ghost guns took some unusual turns Tuesday.