The Supreme Court on Monday ruled that defendants in criminal trials can only be convicted by a unanimous jury, striking down a scheme that has been rejected by every state except one.

The court said in a divided opinion that the Constitution requires agreement among all members of a jury in order to impose a guilty verdict.

"Wherever we might look to determine what the term 'trial by an impartial jury trial' meant at the time of the Sixth Amendment's adoption-whether it's the common law, state practices in the founding era, or opinions and treatises written soon afterward-the answer is unmistakable," Justice Neil Gorsuch wrote in an opinion. "A jury must reach a unanimous verdict in order to convict."

Oregon is the only state left in which defendants can be convicted over the dissent of up to two jurors. Louisiana recently abandoned the practice after more than a century of use.

The ruling overturns the 2016 conviction of a Louisiana man named Evangelisto Ramos. A jury by a 10-2 margin found him guilty of killing a woman in New Orleans. Two years after Ramos's conviction, Louisiana voters approved a constitutional amendment getting rid of non-unanimous jury verdicts.

The new ruling likely means that Ramos could get a new trial.

"We have been bringing challenges to Louisiana's outlier split jury rule to the U.S. Supreme Court since 2004," Ben Cohen, one of Ramos's attorneys, said in a statement. "We are heartened that the Court has held, once and for all, that the promise of the Sixth Amendment fully applies in Louisiana, rejecting any concept of second-class justice. In light of the COVID-19 crisis, it is essential that prisoners who are wrongfully incarcerated be given the chance for release as soon as possible."

Cohen, a lawyer with the Promise of Justice Initiative, said the Louisiana-based nonprofit is working to identify convicts in the state who are in prison despite non-unanimous jury verdicts.

Five justices joined Gorsuch in ruling the practice unconstitutional, though they were divided on certain portions of the decision. Chief Justice John Roberts, Justice Samuel Alito and Justice Elena Kagan dissented from the decision.

In a dissent, Alito said it was wrong for the court to overturn a 48-year-old decision that allowed states to implement non-unanimous jury laws.

"Lowering the bar for overruling our precedents, a badly fractured majority casts aside an important and long-established decision with little regard for the enormous reliance the decision has engendered," Alito wrote. "If the majority's approach is not just a way to dispose of this one case, the decision marks an important turn."

The majority argued that the non-unanimity rules in Oregon and Louisiana were racist, implemented as part of an effort to make it easier to convict black people and other ethnic minorities and to dilute their influence on juries.

"On what ground would anyone have us leave Mr. Ramos in prison for the rest of his life?" Gorsuch wrote. "Not a single Member of this Court is prepared to say Louisiana secured his conviction constitutionally under the Sixth Amendment. No one before us suggests that the error was harmless. Louisiana does not claim precedent commands an affirmance.

"In the end, the best anyone can seem to muster against Mr. Ramos is that, if we dared to admit in his case what we all know to be true about the Sixth Amendment, we might have to say the same in some others."

Updated at 11:34 a.m.