It shall be unlawful for any person, firm or corporation to intercept or monitor, or attempt to intercept or monitor, the transmission of a message, signal or other communication by telephone between an employee or other agent of such person, firm or corporation and a customer of such person, firm or corporation. The provisions of this section shall not apply if the person, firm or corporation gives notice to such employee or agent that such monitoring may occur at any time during the course of such employment. Any person, firm or corporation violating the provisions of this section shall be guilty of a Class 4 misdemeanor. The provisions of this section shall not apply to any wiretap or other interception of any communication authorized pursuant to Chapter 6 of Title 19.2 (§ 19.2-61 et seq.).