The case involved a pair of men who were convicted on several felony robbery charges, but were also convicted under another federal statute that required significant mandatory minimum sentences for a "crime of violence."
The men in question — Maurice Davis and Andre Glover — argued that the federal law was too vague. The justices on Monday were split in their decision, but ultimately sided with the men.
Justice Neil Gorsuch wrote the majority opinion, and was joined by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan.
Justices Brett Kavanaugh, Clarence Thomas and Samuel Alito and Chief Justice John Roberts dissented.