I know of only one case in which some Supreme Court Justices (in dissent) took the view that international law justified certain speech restrictions. And they didn’t just cite some foreign precedents, or statements by international bodies or international law experts, as tangential support in an opinion that focused predominantly on domestic precedents and purely domestic legal disputes. Rather, they specifically endorsed the view that complying with international law justified what might otherwise be an unconstitutional speech restriction.
What was the case, who were the Justices, and who was the judge who wrote the opinion in the court below, which took the same view?