Over the weekend the Post broke a remarkable story about an ongoing Justice Department investigation into a 2009 leak of classified information about North Korea. Investigators did more than just gather phone records, as happened in the probe of leaks to the Associated Press that’s gotten so much attention. In this case, the Justice Department aggressively tracked the comings and goings of a reporter — Fox News’s James Rosen — and obtained a search warrant to examine his emails.

An affidavit in the case even argued that the reporter may be “an aider, abettor and/or co-conspirator.”

This sort of leak investigation is having a direct chilling effect on the ability of investigative reporters to do their jobs, one top investigative journalist said in an interview today.

Mark Mazzetti, who covers national security for the New York Times — one of several leading investigative reporters I reached out to today — says he is experiencing a greater reluctance on the part of sources to talk to him.

“There’s no question that this has a chilling effect,” Mazzetti said. “People who have talked in the past are less willing to talk now. Everyone is worried about communication and how to communicate, and [asking if there] is there any method of communication that is not being monitored. It’s got people on both sides — the reporter and source side — pretty concerned.”

Mazzetti, who’s been reporting on national security since 2001, suggested that what we’re seeing under the Obama administration, which has investigated an unprecedented number leak cases, is something new. He noted that a kind of unwritten consensus existed under the Bush administration that even if officials were angry about leaks, probes into them never really ended up leading anywhere.

“There has been in national security reporting for decades a sense that reporters can talk to government officials to get information, and that it is very important to have information in the public realm from reporters about how government works,” Mazzetti said.

Though all of this seems to originate from the Justice Department, Obama is known to personally hate leaks, and as Ben Smith noted recently, all of this is coinciding with new technological breakthroughs to create what may be an unprecedented level of tracking the dissemination of information to reporters.

In the case of the leaker of sensitive information about North Korea, this may have crossed another line into territory where the reporter is a direct target.

Asked if he thought the Obama administration approach is explicitly about chilling the flow of information to reporters, Mazzetti said: “It certainly seems like they’re being very serious about hunting down people talking to reporters. All we know are the results. The fact that you have so many [cases] now, it scares people who talk to us. [Sources] who might have talked to us once may not talk to us now.”

Said Mazzetti: “Those of us doing national security reporting feel it’s a very difficult climate to work in right now.”

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.