In the first major abortion case before the U.S. Supreme Court since Roe v. Wade was struck down two years ago, the justices will weigh the future of the abortion pill mifepristone on Tuesday as they hear arguments over whether the Food and Drug Administration lawfully relaxed restrictions to make it easier to access the drug to end a pregnancy.

Alliance for Hippocratic Medicine, a group of anti-abortion medical organizations, alleges the FDA failed to adequately consider the dangers of mifepristone when it eased rules in 2016 and 2021, violating a requirement that government agencies act reasonably and explain their decisions to the public.

The case thrusts the high court back into the center of the nation's abortion debate after its conservative majority voted to overrule Roe in 2022 and purported to return "the issue of abortion to the people's elected representatives."

The outcome of the FDA case could sharply limit access to abortion nationwide, even in states that still allow it. Fourteen states have banned abortion in almost all circumstances.

More than half of all abortions in the U.S. are done via medication, and the method is growing in popularity, according to a recent study from the Guttmacher Institute. Mifepristone has been used by more than 5 million women since it was first approved in 2000, and "serious adverse events are exceedingly rare," the FDA says.

The latest guidelines allow mifepristone to be prescribed by doctors, nurse practitioners or physician assistants and distributed in-person or by mail up to 10 weeks of pregnancy.

Prior to 2016, mifepristone could be prescribed only by a physician and dispensed in-person at a medical facility, up to seven weeks of pregnancy. Three in-person doctor office visits were required.

"The agency removed numerous interrelated safeguards without studies examining the changes as a whole or explaining why cumulative studies were unnecessary," the challengers wrote to the court in their brief. "These arbitrary and unreasonably explained agency actions fall far short of what the [law] requires."

The Biden administration, which is defending the pill, says the FDA conducted an "exhaustive review" of scientific evidence and reasonably concluded the drug remains widely safe and effective under the revised conditions of use.

"Few drugs have been so extensively studied after their approval by FDA and can boast such a clear and compelling record of safe use," the nation's 16 leading medical societies, including the American College of Obstetricians and Gynecologists, the American Medical Association, and the American College of Physicians, told the court in a joint filing.

"The scientific evidence is overwhelming: major adverse events occur in less than 0.32% of patients," they wrote. "The risk of death is almost non-existent."

The administration also argues that members of the anti-abortion Alliance -- which do not prescribe mifepristone -- are not directly harmed by the FDA regulations and lack standing to challenge them in court.

"Their primary theory is that their members could be forced to violate their consciences by completing an abortion for a woman with an ongoing pregnancy, but that scenario rests on a chain of speculative contingencies," the administration wrote in its brief to the Court. "Respondents have not identified even a single case in which any association member has been required to provide such treatment."

Between 2.9% and 4.6% of women who took mifepristone later visited an emergency room, according to FDA data. Surgical intervention has been required in 7.9% of cases.

Legal experts say the case -- the first time a court has second-guessed an FDA drug approval -- could have sweeping implications far beyond abortion.

Danco Labs, the leading manufacturer of mifepristone, has warned that an adverse ruling could encourage any medical organization to "challenge virtually every government regulation that touches on health or safety."

The company also said in court filings the case threatens to "destabilize the pharmaceutical industry, which relies both on FDA's ability to make predictive judgments and on courts not second-guessing those scientific judgments."

"This case has the potential to upend regulatory certainty," said Diana Salgado, senior director of public policy litigation at Planned Parenthood Federation of America. "Patient access to other FDA-approved drugs hangs in the balance in this case."

Two lower federal courts sided with the pill challengers, concluding that emergency room doctors are statistically likely to be impacted by the FDA regulation change by having to treat women experiencing adverse side effects from mifepristone -- a scenario that gives them standing to sue.

The Fifth Circuit Court of Appeals further found that FDA did not consider the "cumulative effects" of the drug rule changes in 2016 or 2021 when it reduced the dosing requirements and eliminated mandatory in-person doctor visits for patients using mifepristone. It ordered prior drug safety restrictions reinstated.

The Administrative Procedures Act, the federal law at the center of the case, allows courts to strike down "agency action, findings, and conclusions found to be arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with the law."

If the Supreme Court affirms the Fifth Circuit ruling, access to mifepristone could immediately be curtailed nationwide; however, legal experts have noted, the FDA would still have the opportunity to reissue mifepristone regulations using the protocol laid out by the high court.

A decision in the case is expected by the end of June.