The Supreme Court Monday upheld a Nevada state law barring legislators from voting when they have a personal interest in the outcome, rejecting arguments that such ethics rules infringe on lawmakers' First Amendment rights.

Citing ethics standards dating to 1789, when the first Congress adopted a conflict-of-interest rule, Justice Antonin Scalia's court opinion said a legislator's vote wasn't a form of personal speech. Rather, it was "his apportioned share of the legislature's...