Consistent with our precedent and mandated by separation-of-powers and fair-notice concerns, we hold that an administering agency’s interpretation of a criminal statute is not entitled to Chevron deference. Consequently, the district court erred by finding that the ATF’s Final Rule, which interpreted the meaning of a machine gun as defined in 26 U.S.C. §5845(b), was entitled to Chevron deference. And because we find that “single function of the trigger” refers to the mechanical process of the trigger, we further hold that a bump stock cannot be classified as a machine gun because a bump stock does not enable a semiautomatic firearm to fire more than one shot each time the trigger is pulled. Accordingly, we find that Plaintiffs-Appellants are likely to prevail on the merits and that that their motion for an injunction should have been granted.
Therefore, we REVERSE the judgment of the district court and REMAND for proceedings consistent with this opinion.