FINRA Rule 3110(b)(5) requires firms to have supervisory procedures for capturing, acknowledging, and responding to all written customer complaints, including those submitted electronically. This Rule does not apply to oral complaints; however, in the event of an oral complaint, firms should provide the customer with a form or other format in which he/she can communicate the complaint in writing.
Link to Rule: http://finra.complinet.com/en/display/display_main.html?rbid=2403&element_id=11345
Helpful Link: http://finra.complinet.com/en/display/display.html?rbid=2403&element_id=11470