According to the Department of Justice (DOJ):
“Consensual monitoring is the interception by an electronic device of any wire, oral, or electronic communication where one of the parties to the communication has given prior consent to the monitoring or recording. A warrant is not required to conduct consensual monitoring, and the party providing consent may be a government agent. See 18 U.S.C. § 2511, (2) (c) – (e) (2002).”
In June of 2014, I requested from the NSA, records on their policy regarding “Consensual Monitoring.” It took until September 12, 2017, to get a response, which can be found below.