Despite promises to strengthen protections for whistleblowers, the Obama administration has launched an aggressive crackdown on government employees who have leaked national security information to the press.

With charges filed against NSA leaker Edward Snowden this June, the administration has brought a total of seven cases under the Espionage Act, which dates from World War I and criminalizes disclosing information “relating to the national defense.” Prior to the current administration, there had been only three known cases resulting in indictments in which the Espionage Act was used to prosecute government officials for leaks.

The administration has also targeted journalists. In May, it was revealed that the Department of Justice had secretly seized AP reporters’ phone records while investigating a potential CIA leak, and targeted a Fox News reporter as part of a criminal leak case (outlined below). No journalist has been charged with a crime.

But the news prompted an outcry that Obama’s hard line on leaks could have a “chilling effect” on investigative reporting that depends on inside sources. (In response, the Justice Department issued new guidelines limiting when journalists’ records can be sought.)

A spokesman for the Department of Justice told us the government “does not target whistleblowers.” (Read their full statement.) As they point out, government whistleblower protections shield only those who raise their concerns through the proper channels within their agency — not through leaks to the media or other unauthorized persons.

Director of National Intelligence James Clapper summed up the government’s approach in a 2010 memo: “people in the intelligence business should be like my grandchildren—seen but not heard.”

Here’s a timeline of leak prosecutions under the Espionage Act, showing how they’ve picked up steam under Obama.

Christie Thompson contributed to this story.