A U.S. federal judge dismissed a lawsuit against the FBI over the agency’s controversial practice of spying on California Muslims, arguing the disclosure of a potentially unconstitutional domestic spy program might reveal sensitive state secrets.

District Judge Cormac J. Carney ruled that “the state secrets privilege may unfortunately mean the sacrifice of individual liberties for the sake of national security,” the LA Times reported.

Judge Carney claims to have reached his conclusion after reviewing confidential statements by top FBI officials. The judge ruled that the domestic espionage program – dubbed Operation Flex – involved “intelligence that, if disclosed, would significantly compromise national security.”

The lawsuit was filed jointly by the ACLU and the Council of American Islamic Relations (CAIR) in 2011, on behalf of the Muslim community in Orange Country, California.

The litigants claim the FBI violated their civil liberties by employing an undercover informant, Craig Monteilh, in a dragnet operation that targeted individuals on the basis of their religious beliefs. He infiltrated mosques and installed bugging devices in offices, homes and places of worship.

The plaintiffs vowed to appeal the decision.

Attorneys representing two of the agents being charged say there is little they can do to defend their clients against Monteilh’s accusations due to classified information in the investigation.

ACLU attorney Peter Bibring said the ruling is “terribly unfortunate that there’s a doctrine in the law that allows courts to throw out cases that allege serious constitutional violations based on secret evidence the judge reviews behind closed doors that never sees the light of day,” the LA Times cited him as saying. “That shouldn’t be in a democratic society.”