(1) Employees for which membership in a retirement system is optional may become members by completing an application form provided by the board. The application form must be filed with the board within 180 days of commencement of the employment for which membership is optional, or within 180 days of the effective date of the statute permitting optional membership, whichever is later. Except as provided in (2) , once elected, members may not discontinue membership without termination of employment.

(2) The board may permit an employee to discontinue optional membership if the employee submits proof that the employee was not informed membership was optional. The employee must submit such proof within 180 days of the employee's first day of employment, or within 180 days of the filing of the application form, whichever is later.

(3) Membership discontinued pursuant to (2) must be treated as a reporting error. The board shall issue a credit for all contributions, plus interest, to the employer. The employer will be responsible for refunding appropriate contributions to the employee.