The justices, in a 7-2 ruling, sided with a baker who had faced punishment under a Colorado anti-discrimination law after he refused to make a wedding cake for a same-sex couple, saying it would violate his Christian beliefs.
Nine states have laws allowing state-funded, religiously affiliated adoption agencies to refuse to place children with gay people based on religious beliefs. Republican-governed Kansas and Oklahoma passed such laws this year. Alabama, Mississippi, Michigan, North Dakota, South Dakota, Texas and Virginia all have similar laws.
Legal challenges to those laws, some pending in lower courts, eventually could come to the Supreme Court. The high court's ruling on narrow grounds in favour of baker Jack Phillips did not spell out the circumstances under which religious objections to discrimination claims would have legal merit.
Advocates for gay, bisexual and transgender people sued in Michigan last year over that state's restrictions, imposed in 2015, while a sweeping law passed in Mississippi a year later has already survived one legal challenge.
Separately, Catholic Social Services in Philadelphia sued the city last month after municipal officials stopped placing children with the group, part of the city's Roman Catholic archdiocese, over its religious objections to gay marriage.
American Civil Liberties Union lawyer Leslie Cooper said there was an uptick in conservative-leaning states enacting laws strengthening legal defenses for people who oppose same-sex marriage after the Supreme Court's legalized it nationwide in the landmark Obergefell vs Hodges ruling.
“I think we are seeing the effort to establish a religious right to discriminate in lots of different contexts coming after the Obergefell decision,” Cooper added.
In the adoption context, the baker's victory provided legal ammunition for religious groups facing litigation, according to Matt Sharp, a lawyer with the conservative Christian group Alliance Defending Freedom, which supports religious exemptions to anti-discrimination laws and represented Phillips.
“In my experience, a lot of the rhetoric being tossed around to justify why (private) agencies shouldn't be given (government) contracts has been that they are 'religious bigots,' a lot of the same language directed against Jack,” Sharp said, referring to Phillips.
The Supreme Court ruling made clear “that type of hostility is not permissible,” Sharp added.
The baker case pitted Colorado's law barring discrimination on the basis of race, sex, marital status and sexual orientation against the rights to freedom of speech and expression under the US Constitution's First Amendment. Twenty other states have anti-discrimination laws like Colorado's.
The Supreme Court ruled in favour of Phillips on the basis that the Colorado Civil Rights Commission had shown a hostility toward religion in weighing the case, violating his First Amendment religious rights.
A pivotal justice
The ruling steered clear of endorsing religious-based exemptions to a wide-range of anti-discrimination laws. Justice Anthony Kennedy, who wrote the ruling, made it clear that gay rights and religious rights both should be respected.
The long-term fate of legal challenges to various conservative-backed religious freedom laws could rest on Kennedy, an 81-year-old conservative who sometimes sides with the court's liberals in major cases and has been a champion of gay rights.
If he were to retire from the lifetime post, President Donald Trump could appoint a more conservative replacement perhaps less receptive to gay rights claims.
Under Oklahoma's law, private agencies that handle adoption and foster care cannot be forced to participate in placing a child "when the proposed placement would violate the agency's written religious or moral convictions or policies."
Mississippi's 2016 law is even broader, letting businesses refuse to provide marriage-related services to same-sex couples and allowing judges, magistrates and justices of the peace to refuse to perform same-sex weddings due to religious objections.
Other conservative states have not yet followed Mississippi's lead by passing such a wide-ranging law. Advocates on both sides said conservative lawmakers may have been deterred by the backlash among businesses and others to North Carolina's so-called bathroom bill.
That law, enacted in 2016 and later partially repealed, required transgender people to use bathrooms that correspond to their gender at birth in government buildings and public schools.
Nine states — California, Maryland, Massachusetts, New Jersey, Nevada, New York, Oregon, Rhode Island and Wisconsin — have laws that specifically prohibit discrimination based on sexual orientation in adoption or foster care or both. — Reuters