Bill Raftery (Gavel to Gavel) points out that two state constitutions require supermajorities to invalidate laws on constitutional grounds — the North Dakota Constitution,
The supreme court shall consist of five justices…. [T]he supreme court shall not declare a legislative enactment unconstitutional unless at least four of the members of the court so decide….
and the Nebraska Constitution,
The Supreme Court shall consist of seven judges…. No legislative act shall be held unconstitutional except by the concurrence of five judges.
There is a move, Raftery reports, to statutorily impose a similar 5/7 supermajority requirement in Iowa, where the constitution provides that the surpeme court “shall constitute a court for the correction of errors at law, under such restrictions as the general assembly may, by law.”
Query whether such provisions are constitutional when it comes to questions whether a state statute violates the federal Constitution; state court judges have an independent duty to apply the federal Constitution (“This Constitution … shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding”), and it’s not clear whether that includes applying it using traditionally recognized means of legal decisionmaking, such as simply majority rules. Cf. Debacker v. Sigler (Neb. 1970) (Spencer, J., dissenting) (arguing that the Nebraska supermajority requirement is unconstitutional as to federal claims, “in that it hampers the assertion of a federal right and unreasonably discriminates against litigants asserting the constitutional invalidity of legislation”). My former colleague Evan Caminker summarizes the issue thus:
On the one hand, the [state supermajority voting] protocol applies to state and federal constitutional claims equally, so the protocol neither discriminates against nor appears motivated by hostility to the federal claim. Compare Testa v. Katt, 330 U.S. 386 (1947) (at minimum, a state court cannot discriminate against a federal claim or refuse to consider it based on policy objections); Howlett v. Rose, 496 U.S. 356 (1990) (same). On the other hand, the protocol does mean that the state courts are not “open to” federal claims against state statutes on the same terms as their counterpart federal courts are, a concern that the Court sometimes recognizes as a problem of federal preemption to the extent the state procedure seems to frustrate the enforceability of a federal claim. See Felder v. Casey, 487 U.S. 131, 141 (1988) (state cannot impose procedural rule that “burdens the exercise of the federal right” in a manner that is “inconsistent in both design and effect with the compensatory aims of federal civil rights laws”). Of course, those who argue that state courts in general are less hospitable to federal claims than are federal courts because of different institutional features (such as electoral accountability versus life tenure) might be hard-pressed to distinguish between such institutional features that purportedly influence atomistic judicial determinations and a voting protocol that influences the corporate outcome those determinations produce.
And he adds that South Carolina has, at least theoretically, “an interesting hybrid protocol that combines a supermajority rule in the first instance with a sophisticated majoritarian default plan in the event of insufficient consensus”:
Five Justices sit on the South Carolina Supreme Court. If at least three of them believe that a given case presents an issue of state constitutional law or a potential conflict between state and federal law, the supreme court can resolve the conflict by itself only if the five Justices unanimously agree as to the proper resolution. If not, then the court is enlarged by adding to these five Justices all of the state’s circuit court judges (excluding any that already heard the case below). This new mega-court then decides the case based on simple majority rule. So, a state or federal constitutional challenge to a state statute can succeed in the original supreme court only by unanimous vote, but failing this, it can also succeed in the supplemented court by majority vote.
I describe this protocol as “on the books” because it appears not to be followed in practice…. [T]he five-Justice court does occasionally resolve constitutional challenges with non-unanimous votes. See, e.g., State v. White, 560 S.E.2d 420 (2002) (rejecting constitutional challenge by four-to-one vote); Lee v. S.C. Dept. of Natural Res., 530 S.E.2d 112 (2000) (rejecting constitutional challenges by three to two vote). For a potential explanation, see Jean Hoefer Toal et al., Appellate Practice in South Carolina 4 (1999): “In addition to sitting as a five-member court, the Supreme Court may conceivably convene an en banc court composed of the members of the Supreme Court, as well as those of circuit courts. However, it is an open question whether the statutes allowing the Supreme Court to sit en banc are constitutional. The 1895 South Carolina Constitution made explicit mention of the Supreme Court sitting en banc, but the 1973 revision of Article V, § 12, eliminated all references in the Constitution to the en banc court. The Supreme Court has not sat en banc since the beginning of the twentieth century.”