(LOA) - Legal authority from subscriber to a third party allowing them to act on the third party's behalf regarding matters involving the LEC and / or IXC's.
A letter allowing a person or business to act on behalf of another.
A Letter of Agency is a document authorizing a telecommunications provider to act on your behalf. This is generally required in the United States when switching a telephone service provider while keeping the current telephone number or any other service which requires transfer of information from one provider to another. The regulations governing this are maintained by the FCC.