The Supreme Court on Wednesday struck down a Texas law that banned most abortions after six weeks of pregnancy, ruling that it violated the constitutional right to abortion established in Roe v. Wade.

The 5-4 decision, with Chief Justice John Roberts joining the court’s three liberal justices and Justice Brett Kavanaugh, was a major victory for abortion rights advocates who had challenged the law as an unprecedented assault on reproductive freedom.

The law, known as S.B. 8, had effectively shut down most abortion clinics in Texas since it took effect on Sept. 1. It empowered private citizens to sue anyone who performed or aided an abortion after a fetal heartbeat was detected, and offered them at least $10,000 in damages for each successful lawsuit.

The majority opinion, written by Justice Stephen Breyer, said that the law’s enforcement scheme was designed to evade judicial review and create “a near-categorical ban on abortions beginning six weeks after a woman’s last menstrual period.”

“The statute makes clear that its purpose is to prevent women from exercising their constitutional right to choose abortion,” Breyer wrote. “It is thus inconsistent with the federal Constitution.”

The court’s three most conservative justices — Clarence Thomas, Samuel Alito and Neil Gorsuch — dissented, arguing that the court lacked jurisdiction to hear the case and that the plaintiffs had not shown they faced imminent harm from the law.

“The court’s order today is stunning,” Alito wrote. “Presented with an application to enjoin a flagrantly unconstitutional law engineered to prohibit women from exercising their constitutional rights and evade judicial scrutiny, a majority of justices have opted to bury their heads in the sand.”

The ruling came after the court had initially declined to block the law in a 5-4 vote in September, sparking widespread criticism and protests from abortion rights supporters. The court then agreed to hear oral arguments on Nov. 1, after the Biden administration and a group of abortion providers filed separate lawsuits challenging the law.

The court’s decision on Wednesday did not resolve the underlying constitutional question of whether states can ban abortions before fetal viability, which is generally around 24 weeks of pregnancy. The court is expected to rule on that issue by next June, when it issues its opinion in a separate case involving a Mississippi law that bans most abortions after 15 weeks.

Abortion rights advocates hailed the court’s ruling as a temporary relief for millions of women in Texas who had been denied access to safe and legal abortion care. They also urged Congress to pass legislation that would protect abortion rights nationwide, regardless of state laws.

“Today’s ruling is a critical step in restoring essential health care to millions of people across Texas — but it is not enough,” said Alexis McGill Johnson, president and CEO of Planned Parenthood Federation of America. “We need federal action now to stop these attacks once and for all.”