The Pentagon has told journalists they must agree not to disclose unauthorised information or else risk losing access to the building.
The change is among a number of new restrictions, which also seek to impose limits on the movement of journalists within the facility, which is home to the Department of War, formerly known as the Department of Defense.
It follows a series of leaks in recent months.
Pete Hegseth, who was recently given the new title of Secretary of War, said on social media: "The 'press' does not run the Pentagon — the people do. The press is no longer allowed to roam the halls of a secure facility. Wear a badge and follow the rules — or go home."
The new restrictions were set out in a briefing note sent to members of the press, which they will be required to sign in order to maintain their Pentagon press credentials.
