It is required (read mandatory) to sign a non - disclosure agreement when asked for by the other side since it is based on the sharing of confidential information and therefore it is pertinent for the parties to sign the agreement to show their assent.

Examples of these include the "Classified Information Nondisclosure Agreement," the SF 312. The President of the United States first established this requirement in a directive that states: "All persons with authorized access to classified information shall be required to sign a nondisclosure agreement as a condition of access." This requirement is reiterated in the executive order on classified national security information.