(Reuters) - A U.S. federal judge on Tuesday blocked Missouri from enforcing a law banning abortion in the state after eight weeks of pregnancy except in cases of medical emergency, acting just a day before the law was set to take effect.

U.S. District Judge Howard Sachs in Kansas City temporarily halted the law, pending litigation or a further order of the court, saying it would negatively impact the rights of hundreds of women.

The ban, like ones blocked in Arkansas and Ohio earlier this summer, was written in the knowledge it would likely be struck down but with the hope it would prompt the U.S. Supreme Court to review its landmark 1973 decision legalizing abortion nationwide.

“While federal courts should generally be very cautious before delaying the effect of State laws, the sense of caution may be mitigated when the legislation seems designed, as here, as a protest against Supreme Court decisions,” the judge wrote.

A spokesman for Missouri Attorney General Eric Schmitt said in a statement his office was reviewing Sachs’ ruling before deciding on its next step.

Women’s healthcare provider Planned Parenthood and the American Civil Liberties Union (ACLU) sued Missouri over the law, arguing it was in effect an outright ban on abortion as many women do not know they are pregnant at eight weeks.

“Today’s decision affirms that abortion is still a constitutional right, and we will do everything possible to keep it that way,” said Andrew Beck, an ACLU attorney.

Sachs left in place, at least for now, the law’s prohibitions on abortion for reasons of race, sex or a suspected diagnosis of Down syndrome in the fetus.

“These severe restrictions on abortion access do nothing to address disability rights or discrimination,” said Alexis McGill Johnson, acting president of Planned Parenthood. “They only stigmatize abortion and shame the people that seek that care.”

The law declares Missouri a “sanctuary of life” that protects “pregnant women and their unborn children.” It does not make exceptions for cases of rape and incest, and includes a provision triggering a statewide abortion ban if the Supreme Court overturns its 1973 Roe v. Wade ruling.

Missouri has been at the center of the nation’s escalating abortion debate, as Planned Parenthood is fighting a state health department decision not to renew the license of the provider’s clinic in St. Louis, the only abortion clinic in the state.