WASHINGTON – The protection that abortion enjoys in America despite challenges on the state level is largely due to a federal requirement that all restrictions contain an exception for the life or health of the mother. The case that the Supreme Court will hear today presents a challenge to this legal mechanism, as the justices will hear arguments for and against a New Hampshire abortion law that lacks such an exception for minors.

The case, Ayotte v. Northern New England, was filed after the Boston-based federal Appeals Court for the First Circuit ruled that New Hampshire’s parental notification statute is unconstitutional on the grounds that it does not contain an exception for the life or health of the mother.

New Hampshire’s attorney general, Kelly Ayotte, will argue today that the law does not include a health exception precisely because minors and adult women are viewed differently under the law. Opponents of the statute argue that the current law puts some minors in jeopardy by requiring them to file a lawsuit if they are denied an abortion.

Such life and health exceptions have been a standard requirement for any attempt to regulate abortion since 1973, when the Supreme Court ruled in Doe v. Bolton that a right to abortion exists even in cases where a doctor thinks it’s necessary to preserve a woman’s physical or mental health.

Five years ago, in Stenberg v. Carhart, the Supreme Court struck down more than two dozen state laws prohibiting so-called partial birth abortions because the laws did not contain the same health exception language prescribed by the 1973 case. At issue in today’s case is whether the health exception that applies to women applies to minors too.

“If health means that the woman can say her mental health will be affected if she doesn’t have an abortion and that she is the sole judge of that, then it’s an exception that engulfs the rule,” a professor of law at George Mason University, Ronald Rotunda, said. “But we don’t know if that’s what the Supreme Court means. It will be interesting to find out.”

Tensions over the health exception have been smoldering since Stenberg v. Carhart, when Justice O’Connor provided the crucial swing vote in striking down partial-birth abortion bans solely on the grounds that they did not include a health exception. Justice Kennedy, who upheld the right to an abortion eight years earlier, wrote an angry dissent in which he said the absence of a health exception does not constitute an undue burden.

In his dissent, Justice Kennedy indicated that he would uphold a statute that did not contain a health exception. If, in keeping with his dissent in Stenberg v. Carhart, he decides to uphold the New Hampshire law, then the case would likely end in a tie among the current eight justices. Supreme Court nominee Samuel Alito, if confirmed, would then hear the case next year and participate in a ruling over the summer.

Defenders of the New Hampshire law are quick to point out that it does not present a direct challenge either to abortion rights or to health exceptions as they relate to adult women. Yet backers of abortion rights have already lined up in opposition of the law on the ground that it represents a potential erosion of the health exception and, ultimately, of federal abortion rights.

“This case is an excellent example of a state chipping away at Roe,” the president of the Center for Reproductive Rights, Nancy Northrup, said. “If they say that you don’t need to have an emergency health exception, it would be like taking an ax at one of the core branches of Roe because for 32 years the court has said that women’s health has always taken primacy.”

Some legal scholars agreed. An associate professor at the Notre Dame Law School and the former counsel to the President’s Council on Bioethics, O. Carter Snead, said the case could prove important in chipping away at the health exception rule if and when it is ever challenged head on.

“Given the recent attention to the principles of stare decisis, this case would be noteworthy, perhaps, as an opinion that undermines the doctrinal foundation of the health exception jurisprudence,” Mr. Snead said. “This might be the beginning of a process of redefining the health exception in such a way that will prevent it from being used as an all-purpose device for invalidating any regulation of abortion.”