The Supreme Court is set to hear arguments Tuesday in a case that could reinstate restrictions on the abortion pill mifepristone and sharply roll back access nationwide.

       Being cited in the debate is a 151-year-old law, the Comstock Act of 1873, under which it's illegal to use carriers such as the United States Postal Service to mail "obscene" materials such as drugs that induce abortions.

       Abortion rights advocates are concerned that if former President Donald Trump is reelected, he may be able to utilize the law to undercut access to medication abortion -- which accounted for more than 60% of U.S. abortions last year, according to Guttmacher Institute research -- across the country. Abortion opponents hope the next anti-abortion president, potentially including Trump, would rely on the Comstock Act to pursue more restrictions.

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       Here's what to know about the law's origins, how it was revived in the abortion rights debate following the reversal of Roe v. Wade, and why abortion rights advocacy groups say it may be used to ban the mailing of medication abortion across the country.

       What is the 1873 Comstock Act? The Comstock Act was passed by Congress under the administration of Ulysses S. Grant and criminalized the act of using the U.S. Postal Service to send "obscene" materials such as contraceptives, substances that induce abortion, pornographic content, sex toys and any written material about these items.

       The law is named for Anthony Comstock, head of the New York Society for the Suppression of Vice who was named a special agent of the U.S. Postal Service and was responsible for enforcing the law

       "... [Comstock] would boast about how many people he has arrested, and how many items he confiscated, and how many people he had driven to commit suicide," Mary Ziegler, a law professor at the University of California, Davis, and an expert in the politics of reproduction, history and conservatism in the U.S., told ABC News.

       The Supreme Court of the United States building are seen in Washington D.C., Dec. 28, 2022.

       Celal Gunes/Anadolu Agency via Getty Images, FILE

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       How the Comstock Act relates to SCOTUS case on mifepristone A conservative legal group known as the Alliance for Hippocratic Medicine filed a lawsuit arguing the U.S. Food and Drug Administration's approval of the abortion drug mifepristone should be suspended, or at least severely restricted. The plaintiffs contend that the FDA unlawfully relaxed restrictions on the drug to make it easier to access to end a pregnancy -- and, what's more, that the FDA's decision to allow patients to receive mifepristone by mail instead of in person from certified health providers specifically violates the Comstock Act.

       But the Justice Department has said that the Comstock Act doesn't apply in this case because no one can ever know exactly how a drug will be used when it's mailed.

       Many Republicans in Congress -- 26 senators and 119 representatives -- support the Alliance for Hippocratic Medicine, arguing that the FDA failed to follow proper procedures and federal law when it approved the shipment of abortion medication through telemedicine, according to an amicus brief filed with the Supreme Court in February.

       "The FDA's 2021 action sanctions the shipment of abortion drugs, including through mail-order pharmacies, which violates longstanding federal laws," the brief states. "Congress has barred the abortion industry from using the United States Postal Service to mail abortion-inducing drugs, including the chemical abortion regimen of mifepristone and misoprostol."

       The federal government denies the claim that the FDA acted improperly.

       In a filing to the Supreme Court, the U.S. solicitor general rejected, in detail, the legal challenge to regulation of the abortion pill, arguing the challengers did not "offer any reason to think that changes that had been shown to be safe in varying combinations would become dangerous when combined as a full set."

       White House press secretary Karine Jean-Pierre has said that ruling against the FDA "threatens to undermine the FDA's scientific, independent judgment and would reimpose outdated restrictions on access to safe and effective medication abortion."

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       The Supreme Court is weighing an August 2023 ruling from the 5th U.S. Court of Appeals, which ruled that obtaining mifepristone should require patients to obtain the pill in person, and not through the mail. Before the federal appeals court's ruling, U.S. District Judge Matthew Kacsmaryk -– who was appointed by Trump -- in April 2023 had suspended the FDA's approval of mifepristone. Two of the studies cited in Kacsmaryk's decision have since been retracted by a medical journal.

       Legal experts and abortion rights advocates say they are interested to see whether the Supreme Court chooses to discuss the Comstock Act during oral arguments.

       "I think it's likely that some of the justices, likely the more conservative justices, will bring it up," Ziegler said.

       Pro and anti-abortion protesters are facing off in front of the Planned Parenthood in Washing...Show more ---Show more

       Aaron Schwartz/NurPhoto via Getty Images, FILE

       Implications of the "zombie law" post-Roe Some experts and abortion rights advocates refer to Comstock as a "zombie law," or legislation that has been invalidated by courts but was never fully repealed, leaving room for it to be revived.

       In 1971, Congress removed language from the law that related to contraceptives.

       "The Department of Justice and every court of appeals to consider this issue has been clear that Comstock only applies in the case of unlawful abortions -- so abortions that are illegal under state law -- and all of those Court of Appeals decisions predate Roe," Andy Beck, senior staff attorney for the American Civil Liberties Union Reproductive Freedom Project, told ABC News.

       Following the landmark abortion rights decision by the Supreme Court in 1973, the criminalization of the transportation of abortion drugs still remained on the books. In 1996, members of the House of Representatives failed to repeal the provision related to abortion drugs in the Comstock Cleanup Act, which would have amended the Comstock Act "to repeal a ban on the importation, transportation, or mailing (including through use of a computer) of any material intended for producing abortion or for any indecent or immoral use."

       "Now that Roe v. Wade is gone, that protection against Comstock is gone," said David S. Cohen, a law professor at Drexel University. "Some within the anti-abortion movement are being very explicit about how they want to use Comstock to almost function as a national abortion ban -- without Congress having to lift a finger."

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       Although the Justice Department's Office of Legal Counsel (OLC) issued a memo in 2022 stating that sending abortion pills through the mail is not in violation of the Comstock Act, as long as the drugs are being used lawfully, experts say that determination could easily be ignored -- depending on who is president.

       "There's nothing really stopping anyone from trying to reinterpret it or revive it, even if that's not what the OLC memo says it means, even if that's not what decades of court decisions say it means," Ziegler said. "If you have different courts and different people in the White House, that may not matter."

       ABC News' Devin Dwyer and Anne Flaherty contributed to this report.