A federal grand jury was due to hear evidence Wednesday from witnesses about the passing of state secrets to the WikiLeaks website, NPR reported.
The radio station's website said prosecutors hope to make a case against the website's founder Julian Assange over the disclosure of hundreds of thousands of secret military and diplomatic documents.
It said the case was "part of a much broader campaign by the Obama administration to crack down on leakers."
Steve Aftergood, of the Federation of American Scientists, told NPR he has been following five separate prosecutions.
"For people who are concerned about freedom of the press, access to national security information, it's a worrisome development," Aftergood told the station.
"Leaks serve a very valuable function as a kind of safety valve," he said. "They help us to get out the information that otherwise would be stuck."
"As aggressive as the Obama administration has been in pursuing and prosecuting leakers, the signal that the administration is getting from Congress is, why aren't you doing more?" Aftergood added.
'Never appropriate'
Laura Sweeney, a spokeswoman for the Justice Department, told NPR in a written statement that there were "specific, authorized ways for a government employee to report possible concerns about classified programs."
This included telling "inspectors general, specific Congressional committees and other specified entities."
"It is never appropriate, however, for government employees who are trusted with the nation's most valuable and sensitive information to mishandle classified information in any manner that puts the nation's security at risk," she added.
Award for AssangeMeanwhile, Assange has been awarded the Sydney Peace Foundation's gold medal, an Australian human rights award.
The Sydney Peace Foundation has been awarding prizes for 14 years and some of its highest profile honorees include anti-apartheid icon Nelson Mandela and the Dalai Lama.
Director Stuart Rees told invitees to London's Frontline Club on Tuesday that his foundation's gold medal was meant as a reward for "an unusual act ... that challenges conformity to political or cultural orthodoxy."
"We think the struggle for peace with justice inevitably involves conflict, inevitably involves controversy," Rees said.
"We think that you (Assange) and WikiLeaks have brought about what we think is a watershed in journalism and in freedom of information and potentially in politics," he added.
He also criticized the Australian government, saying it must stop shoring up Washington's efforts to "behave like a totalitarian state," and said it was "appalled by the violent behavior by major politicians in the United States."
Assange is currently in the U.K. fighting extradition to Sweden on sex crime allegations.