When the U.S. Supreme Court decided Roe v. Wade in 1973, it reasoned that women have a right to privacy under the Due Process Clause of the 14th Amendment. What it left open, though, is “issue of the unborn’s humanity,” according to the University of Illinois philosophy professor Peter Wenz. In part because of this ambiguity, case upon case has been litigated to test the limits of the Court’s decision. But what if the justices had decided the case in terms of the First Amendment instead, arguing that abortion rights are a matter of religious freedom?

Here’s why this question is relevant: Even though the Burger Court avoided ruling on the question of fetal personhood in Roe, that issue has featured prominently in subsequent political activism and court decisions related to abortion restrictions. In many of these cases, courts have tried to draw a line after which a woman’s right to an abortion might be outweighed by the state’s interest in protecting the life, or potential life, of a fetus. But, as Wenz argued in a 1992 book declaring abortion rights to be a matter of religious freedom, the definition of fetal personhood is wholly dependent on religious beliefs. So if the government endorses one particular conception of when life begins, it is arguably violating the Establishment Clause by favoring certain religious viewpoints over others—or religion over non-religion, for that matter.

When Roe was argued before the Supreme Court, Catholics comprised almost all of the active opposition to abortion. Many evangelical Christian groups still believed abortion to be a deeply personal matter. It wasn’t until the late 1970s that many of them began to oppose abortion in all cases, except in the most extreme circumstances. After the Roe decision, Catholic groups not only sought allies in other religious communities to bolster their claims against abortion but began to frame those arguments in secular rather than religious terms. Over the course of 30 years, those alliances formed into a veritable political and cultural movement.

Yet, not all religious groups agree with these interpretations of the morality of abortion. Some Jewish traditions teach that abortion is permissible in cases where the health of the mother is at risk, while others allow for abortion in a number of different circumstances. In other denominations like the Church of Jesus Christ of Latter-day Saints, even providing abortion services can lead to excommunication.

In a 2014 Pew Research Center study, the percentage of adults polled who said abortion should be legal in all or most cases varied tremendously by religious affiliation. Eighty-two percent of those who identified as Buddhist and 73 percent of those who identified as Jewish favored legality, compared to only 18 percent of Jehovah’s Witnesses, 27 percent of Mormons, and 33 percent of evangelical protestants.

The discrepancy in views among religious groups was highlighted in a recent amicus brief filed by a group of theologians and ethicists on behalf of an abortion clinic, Whole Women’s Health, in its Supreme Court challenge of a Texas law that imposes severe restrictions on facilities and doctors. The law would require doctors to have admitting privileges at a hospital no more than 30 miles from where they perform abortions and clinic to meet the standards of ambulatory surgical centers. “Because there exists no unified religious or moral position on abortion even within major religions, a state’s attempt to restrict the accessibility of abortion necessarily impinges on the religious and moral decisions of some individuals,” the brief says.

But the religious-freedom argument isn’t often used by those who support abortion rights—the term is most often used by groups who are staunchly pro-life. In 2009, for example, a group of Eastern Orthodox, Catholic, and evangelical Christians institutions drafted the Manhattan Declaration, a “call of Christian conscience” declaring their “obligation” to support "the sanctity of life, traditional marriage, and religious liberty." Since then, signatories have spoken about these causes as if they are inherently linked to one another. And in a number of recent high-profile cases related to abortion and contraception—including 2014’s Hobby Lobby case and the upcoming challenge in Zubik v. Burwell—conservative groups have lobbied for businesses and non-profits to get certain exemptions from federal health-care requirements on religious-freedom grounds.

Some progressive and moderate religious groups feel they have been made invisible by religious conservatives’ claim on the idea of religious freedom. The United Church of Christ, which traces its roots back to the Congregational churches of New England, frequently finds itself explaining to surprised outsiders and newcomers that it supports women’s right to abortion, according to Sandy Sorenson, the director of the UCC’s Justice and Witness Ministries office in Washington D.C. “When you say ‘religious liberty’ nowadays, people think that it means it includes the right to discriminate against people who engage in activities I oppose on a moral basis, or even people’s ways of being that I object to,” Sorenson said. “That’s a huge problem.” The UCC is one of over 25 member organizations in the Religious Coalition for Reproductive Choice, a group that includes Jewish, Catholic, Methodist, Episcopal, and other religious groups advocating for access to abortion.

But the notion of religious freedom may have become so politically charged that progressive groups are reluctant to invoke it. According to Borgmann, a “very big shift” would be needed for the mainstream reproductive-rights movement to begin using arguments linked to freedom of religion. I think it’s probably a combination of it being such a big paradigm shift and a fear of alienating people who aren’t motivated by religion,” she said. “The problem when you’re trying to be really inclusive is that religion can seem very exclusionary or off-putting.” Heather Kimmel, an attorney for the United Church of Christ, agreed. “At this point it’s primarily an intellectual exercise to see what would happen,” she said.

Legally, though, abortion rights based on the First Amendment, rather than the Fourteenth, might be on more solid footing, argue scholars like Wenz. For example: In a concurring and dissenting opinion in the case Webster v. Reproductive Health Services, Supreme Court Justice John Paul Stevens wrote that a Missouri law restricting the use of state funds for abortions violated the Establishment Clause. The law did not violate the clause because it coincided with certain religious viewpoints, he argued, but because there was no “secular purpose” for the law’s assertions.  

On the other hand, nine years earlier in Harris v. McRae, a divided Supreme Court ruled in part that the Hyde Amendment, which restricts government funding of abortion services, does not violate the Establishment Clause of the First Amendment just because the law “may coincide with the religious tenets of the Roman Catholic Church.”

It’s likely, though, that there won’t be many chances to test this theory, particularly in upcoming cases. Pro-choice groups seem loath to use religious-freedom arguments for abortion rights—and today’s left-leaning judges may be equally unenthusiastic. The First Amendment case for abortion rights is a “non-starter,” said Linda Greenhouse, who covered the Supreme Court as a journalist for 30 years and is now a senior research scholar at Yale Law School. “It's an argument that judges just don't want to hear.”