The Sixth Amendment right to jury trial requires that jurors be unanimous in their verdict, the U.S. Supreme Court held April 20, 2020, in Ramos v. Louisiana. 
The Court struck down procedures in Louisiana and Oregon that allowed conviction by non-unanimous juries.
But in reaching the result, the majority agreed on only portions of the Court’s opinion.  And in what many Court observers believed prefaces future opinions, the case produced an unusually high number of concurring opinions – and a dissent – largely debating the justices’ views on stare decisis. 
Evangelisto Ramos was convicted at a jury trial in Louisiana by a 10-2 vote of jurors, and sentenced to life in prison without parole.
Forty-eight states and the federal system require unanimous verdicts.  But Louisiana and Oregon allowed conviction by a less than unanimous vote.
The Supreme Court, in a plurality opinion in Apodaco v. Oregon, in 1972, had upheld the non-unanimous procedure.
But in Ramos, the Court reversed course, in a majority opinion joined, only in part, by six justices.
The majority opinion, by Justice Gorsuch, began by noting that all parties agreed that Louisiana and Oregon’s laws were rooted in racial discrimination.  The Louisiana law was enacted in 1898 “with a careful eye on racial demographics … to ensure that African-American juror service would be meaningless,” the Court said.  Oregon’s law was enacted in the 1930s “to dilute the influence of racial, ethnic, and religious minorities on Oregon juries.”
Turning to the Sixth Amendment itself, the Court said the amendment’s right to a trial by an impartial jury “surely meant something” at the time of its adoption.
“Imagine a constitution that allowed a ‘jury trial’ to mean nothing but a single person rubberstamping convictions without hearing any evidence,” the Court said.  “No:  The text and structure of the Constitution clearly suggests that the term ‘trial by an impartial jury’ carried with it some meaning about the context and requirements of a jury trial.”
“One of these requirements was unanimity,” the Court said.  “Wherever we might look to determine what the term ‘trial by an impartial jury’ meant … the answer is unmistakable:  A jury must reach a unanimous verdict in order to convict.”
The requirement of juror unanimity arose in England in the 14th century, and was a vital right protected by common law, the Court said.  Several early state constitutions expressly required juror unanimity.  It was against this backdrop that the Sixth Amendment was adopted, the Court said.
But “it turns out that the Sixth Amendment’s otherwise simple story took a strange turn in 1972” when a four-justice plurality upheld Oregon’s non-unanimous procedure in Apodaca, the Court said.  “These Justices declared the real question before them was whether unanimity serves an important ‘function’ in ‘contemporary society,” the Court said.  “Then, having reframed the question, the plurality wasted few words before concluding that unanimity’s costs outweighed its benefits in the modern era.”
Not only did this ignore the racially discriminatory origins of the procedure, “the deeper problem is that the plurality subjected the ancient guarantee of a unanimous jury verdict to its own functionalist assessment in the first place,” the Court said.
“No one on the Court today is prepared to say [Apodaca] was rightly decided, and stare decisis isn’t supposed to be the art of methodically ignoring what everyone knows to be true,” the Court said.  “Stare decisis has never been treated as ‘an inexorable command.’” 
“When it revisits a precedent this Court has traditionally considered ‘the quality of the decision’s reasoning; its consistency with related decisions; legal developments since the decision; and reliance on the decision,’” the Court said.  “In this case, each factor points in the same direction” to overrule Apodaca.
Other opinions
Justice Sotomayor concurred, but wrote separately “to underscore three points.” 
“First, overruling precedent here is not only warranted, but compelled,” she said.  “Second, the interests at stake point far more clearly to that outcome than those in other recent cases.  And finally, the racially biased origins of the Louisiana and Oregon laws uniquely matter here.”
Justice Kavanaugh concurred, but wrote separately “to explain my view of how stare decisis applies to this case.”   He said “Apodaca is egregiously wrong, it has significant negative consequences, and overruling it [does] not unduly upset reliance interests.  I therefore agree with the Court’s decision to overrule Apodaca.”
Justice Thomas concurred, as well.  “As I have previously explained, the Court’s typical formulation of the stare decisis standard does not comport with our judicial duty under Article III because it elevates demonstrably erroneous decisions – meaning decisions outside the realm of permissible interpretation – over the text of the Constitution and other duly enacted federal law,” he said.
Thomas also expressed his view that the Sixth Amendment right to unanimous juries “applies to the States through the Privileges or Immunities Clause of the Fourteenth Amendment, not the Due Process Clause.”
Justice Alito, joined by Chief Justice Roberts and Justice Kagan, dissented. 
“The doctrine of stare decisis gets rough treatment in today’s decision,” Alito said.  “Lowering the bar for overruling our precedent, a badly fractured majority casts aside an important and long-established decision with little regard for the enormous reliance the decision has engendered.”
Louisiana and Oregon will now “face a potential tsunami of litigation on the jury unanimity issue,” Alito said.  “More than a thousand defendants” in Oregon alone “may be able to challenge their convictions” on direct appeal, and more challenges will occur in collateral review, he said.
“By striking down a precedent upon which there has been massive and entirely reasonable reliance, the majority sets an important precedent about stare decisis,” Alito concluded.  “I assume that those in the majority will apply the same standards to future cases.”