Sec. 5. MEMBERSHIP. (a) Each regular full-time employee shall become an active-contributory member as a condition of employment and shall make the required deposits commencing with the first pay period in which the employee is compensated following the effective date of this Act. Unless on approved medical leave of absence or on leave to serve in the uniformed services, the employee shall make the deposits as long as the employee remains a regular full-time employee and shall remain a member of the system until the employee or the employee's beneficiary ceases to be entitled to any benefits from the retirement system. The membership for all new regular full-time employees shall commence on the date their employment commences.

(b) Membership in the retirement system consists of Groups A and B, each of which consists of the following groups:

(1) the active-contributory members group, which consists of all members, other than those on authorized leave of absence, who are making deposits;

(2) the active-noncontributory members group, which consists of all employees on approved medical leave of absence and all employees of an employer, other than inactive-contributory members, who have been active-contributory members but who are no longer so because they are not regular full-time employees;

(3) the inactive-contributory members group, which consists of all members who are on an authorized leave of absence and who continue to make deposits into the retirement system during their absence;

(4) the inactive-noncontributory members group, which consists of all members whose status as an employee has been terminated before retirement or disability retirement but who are still entitled to or who may become entitled to, or whose beneficiary may become entitled to, benefits from the retirement system; and

(5) the retired members group, which consists of all members who have retired and who are receiving or who are entitled to receive a retirement allowance.

(c) A member becomes an active-contributory member immediately on resuming employment as a regular full-time employee or on returning from an approved medical leave of absence, as applicable. A member who resumes regular full-time employment is assigned to the group for which the member is qualified under Subdivisions (23A) and (23B), Section 2 of this Act.

(d) It shall be the duty of the retirement board to make a final determination of the membership group to which each person who becomes a member of the retirement system properly belongs. It shall be the duty of the chief administrative officer of each employer to submit to the retirement board a statement showing the name, position, compensation, duties, date of birth, length of employment, and other information regarding each employee of the employer the retirement board may require.

(e) Any person who has ceased to be a member and has received a distribution of the person's accumulated deposits may have the person's membership service in the original group in which the membership service was earned reinstated if the person is reemployed as a regular full-time employee and deposits into the system the accumulated deposits withdrawn by that person, together with an interest payment equal to the amount withdrawn multiplied by an interest factor. The interest factor is equal to the annually compounded interest rate assumed to have been earned by the fund beginning with the month and year in which the person withdrew the person's accumulated deposits and ending with the month and year in which the deposit under this subsection is made. The interest rate assumed to have been earned by the fund for any period is equal to the interest rate credited for that period to the accumulated deposits of members, divided by 0.75.

(f) From time to time the retirement board, subject to the approval of the system's actuary, may elect to permit the reinstatement of membership service forfeited in accordance with the terms of this section.