The Supreme Court agreed Monday to decide another Second Amendment case, U.S. v. Hemani, in which they'll take up the question of whether a federal law that bars gun possession by anyone who is “an unlawful user of or addicted to any controlled substance” violates the Constitution.

The Supreme Court on Monday said it will decide whether a federal law that prohibits unlawful drug users from having firearms violates the Second Amendment, adding a second high-stakes case involving...