A civil liberties group is set to file a motion Thursday asking a special federal court to allow the release of a classified opinion that found the government engaged in unlawful surveillance on Americans.

The Electronic Frontier Foundation is turning to the Foreign Intelligence Surveillance Court after the Justice Department refused to release the court’s opinion under a Freedom of Information Act request.

The opinion’s existence was revealed in July by Sen. Ron Wyden (D-Ore.), who disclosed, with federal officials’ permission, that on “at least one occasion” the court had ruled that the government’s surveillance violated the Fourth Amendment’s protection against unreasonable searches and seizures.

The opinion involved the government’s collection of communications under a 2008 amendment to the Foreign Intelligence Surveillance Act, which broadened the government’s authority to collect e-mails and phone calls of foreign targets in the United States.

The court, which handles applications for surveillance under that law, conducts its proceedings in secret. Its opinions are generally classified.

The Justice Department argued in a separate U.S. District Court proceeding that disclosure of the opinion should be barred because it “implicates classified intelligence sources and methods.”

But it also said that the proper place to seek access to the opinion was the surveillance court itself.

David Sobel, an attorney for the Electronic Frontier Foundation, said the government is playing “a shell game.” He noted that in 2007, when the American Civil Liberties Union asked the surveillance court to release a different opinion, the Justice Department argued that the group should file an FOIA request to the department.

This “DOJ-imposed Catch-22 blocks the public from knowing more about the government’s illegal surveillance,” the group said in a statement.

In a letter to Wyden last year, Kathleen Turner, director of legislative affairs for the Office of the Director of National Intelligence, said the government had “remedied” the surveillance court’s concerns.