The law took effect in Texas at midnight in what advocates say is a major backslide in abortion access rights.
The Supreme Court of the United States has refused to block a Texas law banning abortion after six weeks of pregnancy.
The judges voted 5-4 early on Thursday to deny an emergency appeal from abortion providers and others that sought to block enforcement of the law.
The so-called Heartbeat Act, which went into effect on Wednesday, amounts to a near-total ban on abortion in Texas.
Signed by Republican Governor Greg Abbott in May, the law prohibits abortions once medical professionals can detect cardiac activity, usually about six weeks and before most women know they are pregnant.
Abortion rights groups say such a ban has never been permitted in any state since the Supreme Court decided Roe v Wade, the landmark ruling that legalised abortion nationwide in 1973.
The Supreme Court said its ruling does not make any conclusions on the constitutionality of the Texas law and allows legal challenges to the legislation to move forward.
“In reaching this conclusion, we stress that we do not purport to resolve definitively any jurisdictional or substantive claim in the applicants’ lawsuit,” the majority said in the unsigned order.
“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.”
Chief Justice John Roberts, Justice Stephen Breyer, Justice Sonia Sotomayor and Justice Elena Kagan dissented.
Sotomayor called the majority’s decision “stunning”.
“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,” she said in her dissenting opinion.
Abortion providers challenging the law have vowed to “keep fighting this ban until abortion access is restored in Texas”.
US President Joe Biden called the ruling “an unprecedented assault on a woman’s constitutional rights under Roe v Wade, which has been the law of the land for almost fifty years.”
“For the majority to do this without a hearing, without the benefit of an opinion from a court below, and without due consideration of the issues, insults the rule of law and the rights of all Americans to seek redress from our courts,” Biden said in a statement.
He added he will look into “what steps the Federal Government can take to ensure that women in Texas have access to safe and legal abortions as protected by Roe”.
Texas SB8 will impair women's access to health care and, outrageously, deputizes private citizens to sue those they believe helped another person get a banned abortion.
It's a blatant violation of the right established under Roe V. Wade. We will protect and defend that right.
— President Biden (@POTUS) September 1, 2021
Nancy Northup, the head of the Center for Reproductive Rights, said her organisation was “devastated that the Supreme Court has refused to block a law that blatantly violates Roe v Wade”.
“Right now, people seeking abortion across Texas are panicking – they have no idea where or when they will be able to get an abortion, if ever,” she said in a statement. “Texas politicians have succeeded for the moment in making a mockery of the rule of law, upending abortion care in Texas, and forcing patients to leave the state – if they have the means – to get constitutionally protected healthcare. This should send chills down the spine of everyone in this country who cares about the constitution.”
In Texas, Julia Kaye, a lawyer with the American Civil Liberties Union’s Reproductive Freedom Project, told Al Jazeera there was “devastation and chaos” in Texas as a result of the ban.
“There are thousands of pregnant Texans who are sitting at their kitchen tables trying to crunch the numbers and figure out how they can possibly travel hundreds of miles out of state, in order to get time-sensitive medical care,” she said.
Communities of colour and low-income Texans would be hardest-hit by the new law, she added.