When the U.S. Supreme Court mandated legal recognition of same-sex marriage in the 2015 Obergefell v. Hodges decision, the majority opinion argued that doing so "would pose no risk of harm" to those who disagreed with it.

In his dissent, however, Chief Justice John Roberts suggested that serious religious liberty issues had been left unanswered by the majority, and that the country would ultimately have to contend with the question of how individuals who object to the recognition of same-sex marriage should be treated.

"Hard questions arise when people of faith exercise religion in ways that may be seen to conflict with the new right to same-sex marriage-when, for example… a religious adoption agency declines to place children with same-sex married couples," he said.

In just four years, Roberts' prediction has become a reality. Last week, the Supreme Court was asked to hear a case regarding the city of Philadelphia ending a contract with a Catholic foster agency because it was unwilling to place children with couples in a same-sex marriage.

Catholic Social Services, run by the Archdiocese of Philadelphia, notes that no same-sex couple has ever sought certification through the agency and been denied. If such a couple were to do so, the agency says it "would refer the couple to one of 29 other agencies in Philadelphia-several within blocks of Catholic's headquarters."

Referrals are common, the agency notes, and are routinely carried out for reasons including geographic proximity, a specific agency's medical or behavioral expertise, language needs, or a specialization in pregnant youth or other types of foster situations.

The case contains echoes of another Supreme Court case – the June 2018 ruling in Masterpiece Cakeshop v. Colorado Civil Rights Commission, in which the Court ruled 7-2 in favor of Colorado cake baker Jack Phillips, who in 2012 declined to bake a cake for a same-sex wedding, because of his religious objections to same-sex marriage.

Phillips maintained that he was not declining service because of his clients' sexual orientation, but because he objected to the ceremony in which they were asking him to participate. He said that he would happily create a birthday cake or a graduation cake for a gay client, but that he would not make a cake for a gay wedding. A devout Christian, he also refuses to bake cakes for bachelor parties, divorce parties, and Halloween.

In the Philadelphia case, Catholic Social Services is arguing that certifying a home study for a same-sex couple - married or not - is a tacit endorsement of the union, which is forbidden by the Catholic faith.

"[Catholic Social Services] sincerely believes that the home study certification endorses the relationships in the home, and therefore it cannot provide home studies or endorsements for unmarried heterosexual couples or same-sex couples," the agency's lawyers argued in a brief.

The Philadelphia case thus addresses head-on the question that has been lingering since Obergefell: Does the principle of religious freedom protect those who say they cannot in good conscience accept legal same-sex marriages?

Catholic Social Services has several strong arguments in their favor.

A key part of the Masterpiece decision was the finding that the Colorado Civil Rights Commission acted with "clear and impermissible hostility" toward Phillips' religious convictions. Catholic Social Services is arguing that they too have faced this impermissible hostility toward religious belief.

They note that the agency was told by city officials to change its religious practices because it is "not 100 years ago" and "times have changed." Officials also instructed the agency to follow the city's view of the "teachings of Pope Francis."

"One of the City's highest officials called a religious organization into a meeting to tell its leaders how to interpret the Pope's teachings, then penalized them when they arrived at the 'wrong' answer," the agency's lawyers argued in a brief.

In addition, the agency says Philadelphia Mayor Jim Kenney has demonstrated "a long history of publicly criticizing the Archdiocese" and once said that he "could care less about the people at the Archdiocese."

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Catholic Social Services also argues that the City of Philadelphia's actions are not neutral, and its policies are not generally applicable.

The city claims that it has a policy requiring foster agencies to provide home studies to every applicant who wants one. However, Catholic Social Services' lawyers argue in a brief, "The City also admitted it never told secular foster agencies about this policy, nor monitored their compliance."

The city also allows exemptions at the commissioner's discretion, without any identifiable written guidelines, but told Catholic Social Services that they would not be getting an exemption.

For these reasons, Catholic Social Services is arguing that the case should be reviewed under the judicial standard of "strict scrutiny," meaning that the government is not permitted to place a substantial burden on free exercise of religion unless there is a compelling state interest for doing so, and the least restrictive means of doing so are used.

In the Obergefell decision, the majority dedicated a paragraph to the question of religious liberty, clarifying that religious groups and individuals maintain the right to "advocate" and "teach" their beliefs against same-sex marriage. Court observers, however, noted that this language reflects a commitment to free speech about religious beliefs, rather than the freedom to put those beliefs into action – to practice or exercise religion, as the First Amendment states.

At the heart of the Philadelphia case is the question of whether the newly-recognized "right to gay marriage" precludes religious individuals and organizations from living out their centuries-old beliefs.

If the Court were to rule in favor of Catholic Social Services, it could have significant implications. A narrow ruling in favor of Catholic Social Services, based on the city's alleged display of hostility toward religion, would affirm the Masterpiece decision and prompt lower courts to examine the language that is used by government officials in similar cases, looking for signs of hostility. In cases where this blatant hostility is absent, courts may be split in their decisions.

If the Supreme Court ruled more broadly, affirming that the principle of religious freedom protects individuals and agencies that object to tacitly endorsing same-sex marriage, it could offer widespread legal protection to wedding vendors of all types – photographers, florists, bakers etc. – as well as adoption agencies, marriage counselors, homeless shelters and other service providers.

A ruling against Catholic Social Services would also have significant repercussions for Christians who object to same-sex marriage, potentially leading wedding vendors and service providers to close their businesses. While such a ruling would be surprising to many observers given the Court's current composition, unexpected results are always possible.

Four years after the Obergefell ruling, it is clear that Chief Justice Roberts was right in suggesting that the larger question of religious freedom and how it relates to same-sex marriage would need to be answered. A ruling in the Philadelphia case, should the Court choose to take it up, could play a significant role in answering that question.