(a) The persons eligible for insurance shall be all of the employees of the employers or all of the members of the unions, or all of any class or classes thereof determined by conditions pertaining to their employment, or to membership in the unions, or to both. The policy may provide that the term "employees" shall include retired employees, and the individual proprietor or partner if an employer is an individual proprietor or a partnership. No director of a corporate employer shall be eligible for insurance under the policy unless such person is otherwise eligible as a bona fide employee of the corporation by performing services other than the usual duties of a director. No individual proprietor or partner shall be eligible for insurance under the policy unless he is actively engaged in and devotes a substantial part of his time to the conduct of the business of the proprietor or partnership. The policy may provide that the term "employees" shall include the trustees or their employees, or both, if their duties are principally connected with such trusteeship.
(b) The premium for the policy shall be paid by the trustees wholly from funds contributed by the employer or employers of the insured persons, or by the union or unions, or by both, or partly from such funds and partly from funds contributed by the insured persons. No policy may be issued on which the entire premium is to be derived from funds contributed by the insured persons specifically for their insurance. A policy on which part of the premium is to be derived from funds contributed by the insured persons specifically for their insurance may be placed in force only if at least seventy-five percent of the then eligible persons, excluding any as to whom evidence of insurability is not satisfactory to the insurer, elect to make the required contributions. A policy on which no part of the premium is to be derived from funds contributed by the insured persons specifically for their insurance must insure all eligible persons, or all except any as to whom evidence of individual insurability is not satisfactory to the insurer.
(c) The policy must cover at date of issue at least one hundred persons and not less than an average of five persons per employer unit; and if the fund is established by the members of an association of employers the policy may be issued only if (A) either (1) the participating employers constitute at date of issue at least sixty percent of those employer members whose employees are not already covered for group life insurance or (2) the total number of persons covered at date of issue exceeds six hundred; and (B) the policy shall not require that, if a participating employer discontinues membership in the association, the insurance of his employees shall cease solely by reason of such discontinuance.
(d) The amounts of insurance under the policy must be based upon some plan precluding individual selection either by the insured persons or by the policyholder, employers, or unions.