40 U.S.C. § 3174

The Administrator of General Services may provide and operate public utility communications services serving any governmental activity when the services are economical and in the interest of the Federal Government. This section does not apply to communications systems for handling messages of a confidential or secret nature, the operation of cryptographic equipment or transmission of secret, security, or coded messages, or buildings operated or occupied by the United States Postal Service, except on request of the department or agency concerned.