Federal prosecutors have subpoenaed New York Times reporter James Risen to testify at the trial of a former CIA operative who allegedly leaked classified information that appeared in Risen’s 2006 book.

The trial of Jeffrey Sterling, set to begin in September, is one of five leak cases brought so far by the Obama administration, which has aggressively sought to stem the flow of government secrets to the press and public.

Risen said he would fight the subpoena, issued late Monday by prosecutors in the Eastern District of Virginia. “I will always protect my sources,” he said, “and I think this is a fight about the First Amendment and the freedom of the press.”

A similar subpoena to compel Risen to appear before a grand jury late last year was quashed by U.S. District Court Judge Leonie M. Brinkema in Alexandria. Sterling was indicted in January.

The string of cases, all brought under the 1917 Espionage Act, threatens to undermine the public’s right to be informed on legitimate matters of government policy, according to advocates for the press and transparency issues.

“The subpoena to Risen significantly ups the ante,” said Steven Aftergood, director of the Project on Government Secrecy at the Federation of American Scientists. “It threatens to turn the administration’s fight against leaks into a broader assault on the press.”

Justice Department spokeswoman Laura Sweeney said that the government “seeks to strike the proper balance between the public’s interest in the free dissemination of information and effective law enforcement.”

The government, she said, makes “every reasonable effort to obtain information from alternative sources before even considering a subpoena to a member of the press.”

At issue is a chapter in Risen's book, “State of War,” in which he described a CIA plan to sabotage Iran’s nuclear program by employing a Russian agent. The Russian was to offer the Iranians weapons blueprints that contained fatal flaws. But because the flaws were obvious and possible to overcome, the plan risked helping an adversary “accelerate its weapons development,” the book said.

In a motion accompanying the subpoena, prosecutors stated that Risen “can authenticate his book and lay the necessary foundation” to admit statements in the book into the trial.

“I think they’re just trying to stick it to Jim,” said Lucy Dalglish, executive director of the Reporters Committee for Freedom of the Press. “I just don’t think they have a better chance of making this subpoena stick than they did in the grand jury context.”