The U.S. Supreme Court on Thursday blocked Louisiana from enforcing a law that women's groups said would leave only a single doctor legally allowed to perform abortions in the state.

By a 5-4 vote, the court said the restrictions must remain on hold while challengers appeal a lower court decision in favor of the law. Chief Justice John Roberts voted with the court's liberal members.

It was the Supreme Court's first significant action on the hot-button issue of abortion since Donald Trump's nominee, Brett Kavanaugh, replaced Anthony Kennedy, who generally voted with the court's liberals to uphold abortion rights.

In Thursday's ruling, Kavanaugh voted with the conservatives — Clarence Thomas, Samuel Alito, and Neil Gorsuch.

Kavanaugh filed a dissent, writing only for himself. He said he would have allowed the law to take effect in order to see whether it would impose a burden on women's access to abortion in the state.

Abortion-rights advocates applauded the court ruling, while opponents expressed disappointment.

“The Supreme Court has stepped in under the wire to protect the rights of Louisiana women,” said Nancy Northup, president and CEO of the Center for Reproductive Rights. “The three clinics left in Louisiana can stay open while we ask the Supreme Court to hear our case. This should be an easy case — all that’s needed is a straightforward application of the court’s own precedent.”

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Benjamin Clapper, executive director for Louisiana Right to Life, said he was disappointed that the law remains on hold. He said supporters of abortion rights have fought “against every common-sense health standard. This is just another example of the extreme lengths the abortion industry pursues to protect abortion-on-demand.”

The high court's decision Thursday was not a ruling on the legal merits of the Louisiana restriction. But the decision to keep the law on hold signals that a majority of the justices have doubts about its constitutionality.

Passed by the state legislature in 2014, the measure requires any doctor offering abortion services to have admitting privileges at a hospital within 30 miles. Two Louisiana doctors and a clinic filed a legal challenge, arguing that it was identical to a Texas law the Supreme Court struck down in 2016. In that ruling, joined by Justice Kennedy, the court said Texas imposed an obstacle on women seeking access to abortion services without providing them any medical benefits.

Chief Justice John Roberts arrives prior to President Barack Obama's State of the Union speech on Capitol Hill on January 28, 2014. Larry Downing / Pool via Getty Images

The Center for Reproductive rights said Louisiana's law would leave only one doctor at a single clinic in New Orleans to perform the procedure, a drastic limitation that "cannot possibly meet the needs of approximately 10,000 women who seek abortion services in Louisiana each year."

But Louisiana officials urged the Supreme Court to let them begin enforcing the law. They said the challengers' claim of harm rested on the fear that clinics would be shut down overnight. "But that is not correct. Louisiana envisions a regulatory process that begins, logically, with collecting information from Louisiana's abortion clinics and their doctors," the state said.

The Supreme Court's 2016 ruling, in a case called Whole Women's Health, said requiring abortion doctors to have hospital admitting privileges was medically unnecessary, given that only a tiny fraction of abortions in the first trimester require hospitalization. By contrast the Texas law caused half the abortion clinics in the state to shut down, forcing women to endure longer travel and increased wait times.

It was the most important abortion ruling in 25 years and blocked similar restrictions in Alabama, Mississippi, Oklahoma, Tennessee, and Wisconsin.

The court’s action Thursday came in a brief unsigned order with no written opinion, so none of the five justices who voted to block enforcement of the Louisiana law explained their reasoning.

Roberts was among the dissenters when the court struck down the Texas law. But the court ruled that it was unconstitutional, and his vote Thursday was consistent with that holding.

In response to the lawsuit over Louisiana's identical law, a federal judge said it was likely unconstitutional and issued a stay, blocking its enforcement. But a three-judge panel of the Fifth Circuit Court of Appeals voted to lift the stay. In a 2-1 ruling, the court said Louisiana's law would present far less of an obstacle than the Texas law would have. Less than one-third of Louisiana women seeking an abortion would face even the potential of longer wait times, the court said.

The appeals court concluded that the Louisiana law would not impose an "undue burden" on access to abortion, which has been the Supreme Court's key legal test for challenges to abortion restrictions for nearly three decades. The lower court's ruling was to have gone into effect February 4, but the Supreme Court put it on hold, giving itself more time to decide what to do.

Kavanaugh said that because Louisiana promised to put the law into effect gradually, he would have waited to see how many doctors were able to get hospital admitting privileges. So far, he said, the two sides in the case have offered only "competing predictions" about its effect.

The stay on enforcement of the law will remain until the challengers bring their full appeal to the Supreme Court. If the court agrees to hear the case, the stay would remain until it issues its decision, which would happen sometime late this year or early in 2020.