"Congress passed the Telephone Consumer Protection Act (TCPA), which contains the requirement that any caller using “artificial or pre-recorded voice” to a mobile phone number must have prior consent from the recipient."

The act doesn't specify that "any caller" must meet the requirement but that a "person" must. "The term “person” includes an individual, partnership, association, joint-stock company, trust, or corporation." The mayor is calling as a representative of The City of New York which doesn't meet this definition.