In the U.S. Supreme Court’s travel ban decision Tuesday, the justices declined the U.S. Justice Department’s request to rule on the power of federal courts to issue nationwide injunctions. But one justice—Clarence Thomas—took up the cudgel, questioning the legality of those injunctions.

“I am skeptical that district courts have the authority to enter universal injunctions,” Thomas wrote. “These injunctions did not emerge until a century and a half after the founding. And they appear to be inconsistent with longstanding limits on equitable relief and the power of Article III courts. If their popularity continues, this court must address their legality.”