The US supreme court will decide as early as Friday whether to hear a case that could tee up the most consequential ruling on abortion rights in 23 years: a challenge to a Texas law that threatens to shut down half the state’s clinics, or an appeal from the state of Mississippi defending a law that would close the only remaining abortion clinic in the state.

The stakes in both cases are towering. A decisive ruling in either one would determine the fate of nearly two dozen abortion clinics across the rural south that are threatened with closure by similar laws. If the justices issue a ruling that strikes down one of the laws, it could halt the record pace of new abortion restrictions flowing out of conservative state legislatures. A ruling the other way would invite even more restrictions and leave little room for abortion providers to challenge those new regulations in court.

“I don’t think it’s overstating the case to say if the court upholds the restrictions in either the Texas or Mississippi case based on the justifications each state is offering – that these are health protective – that it would result in the most drastic reduction of the availability of abortion at any point since Roe v Wade,” said Priscilla Smith, director of Yale Law School’s reproductive justice program.

The court has issued only three decisions on abortion since 1992, all of which pared back existing rights. As a result, advocates have been reluctant to take any abortion case to the supreme court, for fear that it would result in a more expansive and permanent rollback of reproductive rights.

But Amy Hagstrom Miller, the founder of Whole Woman’s Health, the network of abortion clinics that is leading the lawsuit against the state of Texas, said the anti-abortion law that gutted the state’s abortion offerings had forced advocates’ hand.

“We’ve become the beacon for, can we stop this constant drum of abortion restrictions?” she said. “Providers as far as Ohio and Florida and Michigan are hoping our case can bring some relief. All eyes are on Texas.”

The Texas lawsuit, Whole Woman’s Health v Cole, revolves around a 2013 anti-abortion law that has closed more than half of Texas abortion clinics. Texas had 41 abortion clinics before the passage of HB2, as the bill is known. That number dwindled to 22 after a provision of the law took effect requiring abortion providers to have admitting privileges with a hospital no more than 30 miles away. Today there are 20 clinics. A second provision of the bill would further slash the number of providers to nine by requiring all abortion clinics to meet hospital-like “ambulatory surgical center” standards. The four liberal justices of the court and justice Anthony Kennedy have blocked that measure as the court decides whether to take the case.

The other case, Jackson Women’s Health Organization v Currier, centers on a Mississippi law requiring abortion clinics to have admitting privileges at a local hospital. That law would shut down the only abortion provider in the state, which abortion rights advocates say is the underlying intent. The fifth circuit court of appeals has blocked the law, and the state is appealing.

Should the supreme court agree to hear either case, the consequences loom large. Eight states have passed highly similar abortion restrictions that are now mired in court battles. A ruling on the Texas or Mississippi law would in effect end those lawsuits, with implications for some two dozen abortion providers.

Even more crucially, both cases ask the justices to clarify how far a state can go in passing laws that regulate abortion clinics before a measure becomes unconstitutional. Lower courts have been tussling with this question since 1992, when the supreme court ruled in Planned Parenthood v Casey. The decision gave states the right to restrict abortion in the interest of the woman’s health as long as the restriction is not an “undue burden”. But the high court has never clarified the phrase’s meaning.

Whole Woman’s Health is pushing the supreme court to recognize a law as an undue burden if it does not serve an actual health purpose. If the supreme court were to agree, it would force lower courts to scrutinize the evidence behind many new abortion restrictions. Reproductive rights groups and many mainstream medical organizations maintain that there is little medical evidence for the Texas or Mississippi laws and their many copycats. Indeed, courts that have examined the evidence for new restrictions have tended to rule against abortion foes.

“The question at the heart of both these cases is whether the state can use their stated interest in protecting women’s health as a kind of smoke screen for burdening clinics so much that they shut down,” said Stephanie Toti, a lawyer with the Center for Reproductive Rights and the lead attorney for Whole Woman’s Health.

But a three-judge panel from the fifth circuit court of appeals rejected that argument in June. Instead, the court took Texas lawmakers’ assertion that the law was intended to protect women’s health at face value. Attorneys for Texas argued that the law did not pose an undue burden because “the vast majority of Texas abortion patients live within a 150-mile driving distances of Austin, Dallas, Fort Worth, Houston or San Antonio” – cities that will still have abortion clinics if the law goes into effect. The panel of judges agreed, prompting Whole Woman’s Health to appeal to the supreme court.

More than 50 miles from the nearest clinic

The impact of a supreme court decision would be greatest in Texas, where Whole Woman’s Health operates four clinics – three of which will close if the groups don’t prevail in court. Texas had 41 abortion clinics before the passage of HB2 in 2013.

A decision to uphold the entire law would close all but nine or 10 abortion clinics in Texas, with none remaining in the entire western half of the state. (The 10th clinic is a Whole Woman’s Health location in McAllen; the fifth circuit upheld the admitting privileges rule but allowed that location to remain open because it is the only abortion provider in the Rio Grande valley.)

That would also be the consequence if the supreme court does not agree to wade into the Texas case and simply allows the law to take effect. “If they don’t take this case, that right that exists on paper would be decimated in reality for women in Texas and beyond,” Miller said.

Texas is a state with 5.4 million women of reproductive age. With only a handful of clinics left, researchers have estimated that nearly 2 million women would live more than 50 miles from the nearest abortion clinic. Three-quarters of a million women would live more than 200 miles away. And because wait times for an abortion would skyrocket, the number of second-trimester procedures, which are more expensive, invasive and time-intensive, could double.

If the supreme court upheld the Texas or Mississippi law, similar restrictions blocked by lower courts in six other states are likely to take effect immediately. Alabama, Kansas, Louisiana, Oklahoma, Tennessee and Wisconsin would see some 20 abortion clinics shut down, leaving several states with only one or two clinics. “There suddenly wouldn’t be clinics for hundreds of miles,” said Smith. Several of the clinics that would disappear from the south-east are already shouldering the extra demand from patients in Texas, such as Hope Medical Group in Shreveport, Louisiana. In 2013, a quarter of the clinic’s patients traveled from Texas – up from 15% of all patients in 2011.

Four of five clinics in Alabama and six of seven in Louisiana would close their doors, leaving a stretch of more than 400 miles between northern Alabama and New Orleans without a single provider. Mississippi would become the first state without a single abortion clinic since Roe v Wade, the case that established the right to an abortion almost 43 years ago. And the trend could continue.

“If the supreme court gives the thumbs-up to these types of regulations, you will see other states follow,” said Denise Burke, vice-president of legal affairs of Americans United for Life, which supported the Texas measure. Other anti-abortion proposals, such as those restricting when and where women may use medication to end their pregnancies, may also benefit from a ruling for Texas or Mississippi.

One potential outcome of the Texas or Mississippi cases, in other words, would be to completely rearrange the map for US abortion access.

Engineers of the movement

Miller has a mantra she has been repeating ever since Whole Woman’s Health launched its lawsuit: “We are standing on the right side of history by bringing this case at this time.”

But the timing of Miller’s lawsuit was in some ways chosen for her by the country’s most powerful anti-abortion group, Americans United for Life (AUL).

The group is the foremost legal champion of the anti-abortion rights movement and has written the model legislation for most new anti-abortion regulations passed in the last decade and a half. The Texas and Mississippi laws are not directly based on its model legislation. But AUL bears the lion’s share of responsibility for getting all abortion foes, including the Texas legislature, to speak in terms of the health of the mother. The health justification is now a key part of the state’s case. In a critical departure from its predecessors, who spoke of “baby killers”, AUL has almost always justified its anti-abortion proposals as protective of maternal health.

“We’ve brought the movement to this moment,” said Burke.

Abortion rights advocates argue that ambulatory surgical center and admitting privilege requirements are not necessary to perform safe abortions and do not make abortion safer. They see ASCs, which can cost an abortion provider millions of dollars to build and maintain, as a way of putting abortion providers out of business.

“ASC and privileges requirements do nothing to protect the health and safety of women and are incongruous with modern medical practice,” read a brief submitted to the fifth circuit by the American College of Obstetricians and Gynecologists and the American Medical Association. “Scientific literature suggests that the safety of abortions performed in an office setting is equivalent to the safety of those performed in a hospital setting … HB2’s requirement that abortion facilities meet the standards for ASCs is devoid of any medical or scientific purpose.” The brief noted that most abortions are simple procedures, with no incisions, and the risk of death from abortion is 0.0006%, while only 0.05% to 0.2% of abortion procedures involve major complications.

AUL dismisses this as misinformation from a self-interested and poorly regulated industry. “AUL has led the push for the last 15 years for comprehensive oversight of abortion clinics,” she said. “Now, the court is being presented with an opportunity to strike a decisive blow for women’s health and safety.”