A Letter of Agency (LOA) is a document authorizing a telecommunications provider to act on a consumer's behalf. Some vendors may also call this a Letter of Authorization, however this is an incorrect name and Letter of Agency is the official term used in FCC documentation and Federal Statute.
The official term for a document authorizing a telecommunications provider to act on a consumer's behalf is "Letter of Agency," as defined in FCC documentation and Federal Statute.  "Letter of Authorization" is an inaccurate alternative name.