New York Times Executive Editor Jill Abramson warned at a Columbia University School of Journalism panel that the federal government’s crackdown on leakers has had a “profound effect on journalism.”

Abramson, who covered the Beltway at the Wall Street Journal and later as the Times’ D.C. bureau chief, noted that there have been seven criminal leak investigations under the Obama Administration, more than twice the number of any previous administration in American history.

The threat of legal prosecution has “effectively criminalized” journalism about sensitive national security issues, she argued Thursday.

“A real freeze is setting in on what had been to this point, I think, a healthy discourse between sources and journalists,” Abramson said.

“Journalists are saying, ‘I will go to jail to protect your identity,'” she added. “These words are now being uttered.”

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Abramson’s reflections came during a panel discussion on how NSA whistleblower Edward Snowden had altered the contours of journalism and raised questions about the limitations of press freedoms. The talk brought together Abramson, the Times’ chief editor; Cass Sunstein, a member of President Obama’s Review Group on Intelligence and Communications Technologies; Janine Gibson, editor-in-chief of The Guardian, which broke the story on NSA surveillance; and David Schulz, a First Amendment lawyer and outside counsel to The Guardian.

Snowden’s revelations that the NSA was mining millions of email and instant messaging contact lists, tracking cell phone calls and spying on allies has set off an international debate about the scope and efficacy of modern surveillance. The government response has been fierce, Gibson noted.

This month, Director of National Intelligence James Clapper insinuated to the Senate Intelligence Committee that journalists harvesting Snowden’s cache of intelligence documents were “accomplices” to a crime. Such remarks inspire a fresh set of concerns when it comes to grappling with confidential sources and material.

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“The sort of basic fact of, ‘Who is your source?’ ‘Well, I’m not going to tell you,’ has become you’re part of a conspiracy possibly involving the KGB or maybe China,” Gibson said. “Because the original, the ordinary way of chilling journalism won’t work…We’re not any more going to be worried about naming names. It’s going to be about proving that you’re not a co-conspirator.”

Schulz said that bureaucratic threats could have unforeseen consequences and may silence stories, such as reports of the CIA’s use of enhanced interrogation techniques or deplorable conditions at Walter Reed Army Medical Center, of which the public should be aware.

“If we don’t have a mechanism that allows whistleblowers, our whole society is going to suffer,” he said. “We can’t count on oversight by Congress and the courts.”

In the case of Snowden, Gibson noted that the 29-year old leaker had an “eerie prescience” about the government’s ability to track him down and characterize him in a negative way.

It was a lesson that may have been gleaned in part from the Wikileaks fallout — one that left two main actors in that drama, Julian Assange and leaker Bradley Manning, profoundly damaged. Yet the fallout went further.

Gibson noted that the British government cracked down hard on the Guardian’s use of secret information about surveillance in the Snowden stories. Outside papers such as the New York Times continued probing the thousands of leaked documents.

Both editors stressed that they take their responsibilities as filters very seriously, with Abramson commenting that when the government raises the issue of national security it causes her paper to “hit the breaks a bit.” Taking journalists out of the equation can work against the government’s interest, they argued.

“The information will find its way out in a way that cannot engage with,” Gibson said.