It shall be unlawful for any executive, administrative, professional or supervisory employee to be a member in, or to be accepted for membership by, any labor organization, the constitution and bylaws of which permit membership to employees other than those in executive, administrative, professional or supervisory capacities or which is affiliated with any labor organization which permits membership to employees other than those in an executive, administrative, professional or supervisory capacity. The provisions of this section shall not be construed so as to interfere with or void any insurance contract in existence and in force on June 29, 1943.