In Ballew v. Georgia, the U.S. Supreme Court ruled that a five-person jury in a criminal trial was unconstitutional as it violated the defendant's Sixth Amendment right to an impartial jury and his Fourteenth Amendment right to equal protection under the law. The case arose when Billy J. Ballew was convicted by a five-member jury for distributing obscene materials in Georgia state court, where juries of less than 12 members were permitted for misdemeanors punishable by imprisonment up to two years or fines up to $1,000. In its decision, the Supreme Court noted that smaller juries are less likely to foster effective group deliberation and could potentially undermine confidence in public acceptance of verdicts due their lack of representativeness compared with larger juries.

In the dissenting opinion for Ballew v. Georgia, Justice Rehnquist disagreed with the majority's ruling that a five-person jury in a criminal trial was unconstitutional. He argued that there was no historical or empirical evidence to support the claim that smaller juries were less likely to safeguard defendants' rights or deliver fair verdicts than larger ones. Furthermore, he contended that it is not within the Court's jurisdiction to determine optimal jury size and criticized his colleagues for overstepping their boundaries by doing so. He also pointed out inconsistencies in previous rulings on similar cases and expressed concern about potential negative impacts of this decision on state courts' ability to manage their caseloads efficiently.