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Washington — The Supreme Court unanimously ruled Monday that the city of Boston violated the First Amendment when it rejected a request from a Christian civic organization to fly a flag bearing a cross on a flagpole outside of City Hall.

Justice Stephen Breyer delivered the opinion for the court, which sided 9-0 with activist Harold Shurtleff and Camp Constitution, a group whose mission is in part to “enhance understanding of our Judeo-Christian moral heritage,” in the free speech dispute. 

The case, known as Shurtleff v. City of Boston, arose in 2017 when Shurtleff, director and founder of Camp Constitution, asked to fly what was characterized as the “Christian flag” outside of Boston City Hall. Since at least 2005, the city has allowed groups to hold flag-raising ceremonies on City Hall Plaza, during which participants can hoist a flag of their choosing on one of the three flagpoles that stand outside the entrance to City Hall.

Throughout the program, flags that have been displayed include those of other countries or flags marking Boston Pride Week. Between 2005 and 2017, the city approved an estimated 50 unique flags that were flown at 284 ceremonies.

Boston did not deny a request to raise a flag until 2017, when Shurtleff asked to hold a flag-raising ceremony at City Hall Plaza to “commemorate the civic and social contributions of the Christian community” and raise a white flag that featured a red Latin cross set against a blue backdrop in the upper left corner, described as the Christian flag.

But the city denied Shurtleff’s request due to concerns that displaying a religious flag outside of City Hall would violate the First Amendment’s Establishment Clause. 

Shurtleff and Camp Constitution then sued, arguing the city’s refusal to allow them to raise their flag violated their free speech rights. A federal district court ruled in favor of the city, finding that flying private groups’ flags from City Hall was government speech, and the city acted within its authority in rejecting Shurtleff’s request. The 1st U.S. Circuit Court Appeals affirmed the trial court’s decision, after which Shurtleff and Camp Constitution appealed to the Supreme Court.

In his opinion, Breyer wrote the case turned on whether Boston’s flag-raising program expressed government speech, and the court concluded that it did not. As a result, the city’s refusal to let Shurtleff and Camp Constitution fly their flag amounted to impermissible viewpoint discrimination in violation of their free speech rights.

“While the historical practice of flag flying at government buildings favors Boston, the city’s lack of meaningful involvement in the selection of flags or the crafting of their messages leads us to classify the flag raisings as private, not government, speech — though nothing prevents Boston from changing its policies going forward,” he said.

In a separate opinion, Justice Brett Kavanaugh wrote: “Under the Constitution, a government may not treat religious persons, religious organizations, or religious speech as second-class.”