A member who is acting as a broker for a customer or for both such customer and some other person, or a member who is acting as a dealer and who receives or has promise of receiving a fee from a customer for advising such customer with respect to securities, shall, at or before the completion of any transaction for or with such customer in any security in the primary or secondary distribution of which such member is participating or is otherwise financially interested, give such customer written notification of the existence of such participation or interest.