[T]he FBI withheld the identities of the electronic communications service providers that have provided information […] to the FBI as part of its national security and criminal investigations under authority granted by Section 702 of the FAA. Exemption (b)(5)-1, cited in junction with (b)(7)(D)-1, has been asserted because disclosure of the identities of electronic communication service providers would cause substantial harm to their competitive position. Specifically, these businesses would be substantially harmed if their customers knew that they were furnishing information to the FBI. The stigma of working with the FBI would cause customers to cancel the companies’ services and file civil actions to prevent further disclosure of subscriber information.

David M. Hardy, declaration in ACLU v. Office of the Director of National Intelligence