WASHINGTON – A sharply divided Supreme Court officially declined late Wednesday to halt a Texas law that effectively bans abortions after about six weeks of pregnancy, meaning the law will remain in force while a coalition led by abortion providers pursues a legal challenge to strike it down.

In a 5-4 decision handed down just before midnight, the five members of the court’s conservative wing ruled that the providers had raised “serious concerns” about the constitutionality of the Texas law. But they said the “complex and novel” procedural questions raised by the unusual design of the law — in which private citizens would enforce it instead of state officials — meant the Supreme Court could not stop it from going into effect Wednesday.

The ruling drew sharp rebukes in dissents from the three justices on the court’s liberal wing, and one from Chief Justice John G. Roberts Jr., who pointed out how Texas lawmakers had designed the law just to evade such a preliminary judicial review.

The four dissenters would have stopped the unprecedented law from taking effect, as Roberts put it, “so that the courts may consider whether a state can avoid responsibility for its laws in such a manner.” Instead, almost exactly 24 hours earlier, with the law taking effect and no word yet from the Supreme Court, most abortions became illegal in Texas under a law that conflicts with long-standing rulings that prohibit bans on abortion before viability, or the time when a fetus could survive outside the womb.

“The Court has rewarded the State’s effort to delay federal review of a plainly unconstitutional statute, enacted in disregard of the Court’s precedents, through procedural entanglements of the State’s own creation,” Justice Sonia Sotomayor wrote in her dissent.

The Texas law bans abortions if a fetal heartbeat can be detected, which occurs around the sixth week of pregnancy. Many patients may not know they are pregnant until after a heartbeat can be found. About 85 percent to 90 percent of Texas abortions occur after six weeks of pregnancy.

The Texas legislature did not set up a typical system where state officials would enforce the law, such as making abortion a crime. Instead, the law allows private citizens to sue abortion providers, physicians, patient support networks and anyone who supports someone getting an abortion, even by driving them to a clinic.

Any individual can bring suit in any Texas court if they suspect someone “aided” in an abortion. The plaintiff would receive a $10,000 “bounty” in the event of a guilty verdict. That structure, along with legal action at the U.S. Court of Appeals for the 5th Circuit, meant the coalition of abortion providers had to take the unusual step of asking the Supreme Court to stop the law before any court had done so.

The Supreme Court leaned heavily on that procedural wonkiness to decide to let the law go into effect despite the concerns about whether it is constitutional. Federal courts can’t stop the implementation of laws themselves, the majority wrote, only the individuals tasked with enforcing those laws. “And it is unclear whether the named defendants in this lawsuit can or will seek to enforce the Texas law against the applicants in a manner that might permit our intervention,” the court’s decision states.

The state represented that it and its employees do not have the authority to enforce the Texas law, the Supreme Court said. It is not clear whether the court can issue an injunction to prevent state judges from deciding lawsuits under the law. And no private citizen has tried to enforce the law in a case before the court.

“In reaching this conclusion, we stress that we do not purport to resolve definitively any jurisdictional or substantive claim in the applicant’s lawsuit,” the Supreme Court wrote. “In particular, this order is not based on any conclusion about the constitutionality of Texas’s law, and in no way limits other procedurally proper challenges to the Texas law, including in Texas state courts.”

‘This is untenable’

The dissents pointed out that letting the law take effect has consequences.

Justice Stephen G. Breyer wrote that allowing the law to take effect could threaten “imminent and serious harm” to women who have a constitutional right to abortion in the first part of a pregnancy. That right was first established in the 1973 decision in Roe v. Wade and sharpened in the 1992 decision in Planned Parenthood v. Casey. Breyer wrote that the state’s providers have stopped abortion procedures after the detection of a heartbeat, with clinics claiming they will be unable to run the financial and other risks that come from waiting for a private person to sue them under the Texas law.

Sotomayor wrote separately that “the majority of Justices have opted to bury their heads in the sand” on a law that is “a breathtaking act of defiance — of the Constitution, of this Court’s precedents, and of the rights of women seeking abortions throughout Texas.”

“Today, the Court finally tells the Nation that it declined to act because, in short, the State’s gambit worked,” Sotomayor wrote. “This is untenable. It cannot be the case that a State can evade federal judicial scrutiny by outsourcing the enforcement of unconstitutional laws to its citizenry.”

And Roberts warned that caution is needed with such an unusual statutory scheme, even if the defendants might prevail, because of the message it might send to other states. “But the consequences of approving the state action, both in this particular case and as a model for action in other areas, counsel at least preliminary judicial consideration before the program devised by the State takes effect,” Roberts wrote.

The legal challenge now sits at the 5th Circuit. Throughout the lawsuit over the Texas law, state officials and others named as defendants argued that the case against them should be dismissed. A district court rejected that argument and held that the case should go forward, setting a hearing about whether to prevent the law from taking effect as the legal challenge proceeded. But the defendants appealed that lack of a dismissal to the U.S. Court of Appeals for the 5th Circuit, which entered an order taking control of the case and canceling the injunction hearing.