The Supreme Court grappled on Monday with the U.S. government’s effort to fend off a lawsuit brought against the FBI over a controversial post-9/11 surveillance operation that targeted a Muslim community in California.

At issue was how courts should handle the government’s assertion of the state secrets privilege, a legal doctrine allowing certain information to be concealed if its disclosure would harm national security.

Several justices appeared to search for a narrow path that might permit the plaintiffs, three Muslim men who were targets of the operation, to pursue their claims against the FBI, while allowing the Supreme Court to defer some of the thornier questions about the scope of the government’s privilege.

The case traces back to 2006, when the FBI launched a 14-month counterterrorism operation aimed at surveilling members of Southern California’s Muslim community. 

The bureau relied on an informant, Craig Monteilh, to pose as a Muslim convert and record his conversations at mosques and during other interactions. Midway through the operation, in a twist of irony, Monteilh began to make provocative statements about jihad that so alarmed his new Muslim acquaintances that they eventually reported him to the FBI.

Monteilh and the FBI later parted ways, and he went public with the details of the operation. The FBI has since confirmed that Monteilh made secret recordings as part of his undercover work.

In 2011, three Muslim men who had been spied on sued the FBI and its agents, alleging that, among other things, they had been illegally targeted because of their religion.

In response, the government invoked the state secrets privilege and asked the judge to dismiss the relevant claims because litigating them would require the disclosure of protected information. The court granted the FBI’s request, prompting an appeal by the plaintiffs.

The San Francisco-based U.S. Court of Appeals for the 9th Circuit reversed the district court’s ruling, siding against the FBI and allowing some of the Muslim plaintiffs’ claims to proceed. 

The appeals court ruled the district court erred by applying court-made rules to decide the government’s privilege claim rather than a procedure provided in the 1970s-era statute called the Foreign Intelligence Surveillance Act.

On Monday, several of the justices explored ways to decide the case in a manner that would not turn on a parsing of the interplay between the competing sets of rules, but rather focus on whether the district judge, who did not review the evidence in question, had dismissed the case prematurely.

“Suppose that the easiest question in this case, I think, is the question ... of when dismissal is appropriate in a state secrets case,” Justice Elena Kagan said during an exchange with the lawyer for the plaintiffs. Making that issue a central focus, she added, “would seem an attractive solution to me.”

A ruling in the case, FBI v. Fazaga, is expected by the end of June.