Mont. Code Ann. § 19-3-412

(1) The Except as provided following in subsection (2), employees the following employees in covered employment may become members of the retirement system at their option at any time during positions that are not elected offices shall elect either to become active members of the their employment in a covered position retirement system or to decline this optional by membership by filing a membership card an irrevocable, written application with the board: board in the manner prescribed

(a) elected officials of the state or local governments who are paid on employees serving in employment that does not cumulatively exceed a salary or wage basis rather than on a per diem or other reimbursement basis; total of 960 hours of covered employment with all employers under this chapter in any

(b) part-time employees serving in employment that does not exceed a total of 960 hours of employment covered directly appointed by this chapter in any fiscal year; the governor;

(c) employees directly appointed by working 10 months or less for the governor; legislative branch to perform work related to the legislative session;

(d) employees working 6 months or the less for the legislative branch to perform work related to the legislative session; chief administrative officer of any city or county; and

(e) the chief administrative officer employees of any city county hospitals or county;

(f) employees of county hospitals or rest homes in counties of the third, sixth, and seventh class.

(2) If an employee declines optional membership, the employee shall execute a statement waiving membership and the employer shall retain the statement.

(2) (a) An employee who is an active or inactive member at the time of employment is not eligible to make an election under subsection (1). Upon employment in the position, an employee who was an active member remains an active member for all covered employment and an employee who was an inactive member shall become an active member.

(b) A person who was a retired member before employment in a position for which membership is optional under subsection (1) is not eligible to make an election under subsection (1) and is subject to the provisions of Title 19, chapter 3, part 11.

(3) (a) The board shall prescribe the form of the written application required pursuant to subsection (1) and provide written application forms to each employer.

(b) Each employee in a position covered under subsection (1) shall obtain the written application form from the employer and complete and return it to the board.

(c) The written application must be filed with the board within 90 days after the commencement of the employee's employment.

(d) The employer shall inform the employee of the option to elect membership and retain a copy of the employee's written application.

(4) Failure to inform an employee in a position covered under subsection (1) of the employee's option to elect membership must be treated as a correction of a reporting error under 19-2-506(4). An employee who elects membership in the defined benefit plan following discovery of an omission to be informed of the optional election may choose to purchase the retroactive service under 19-3-505, and the employer is obligated to pay the employer contributions as well as accrued interest in both the employer and employee contributions.

(5) If the employee fails to file with the board the written application required under subsection (1) within the time allowed in subsection (3), the failure must be considered an election to decline membership.

(6) Except as provided in subsection (7), an employee who declines optional membership may not receive membership service or service credit for the employment for which membership was declined.

(7) An employee who declined optional membership but later becomes a member may purchase service credit for the period of time beginning with the date of employment in which membership was declined to the commencement of membership. Purchase of service credit pursuant to this subsection must comply with 19-3-505.

(8) An employee who has made an election under this section may not make a new or different election under this section in any circumstance unless the employee has been terminated from employment in all optional membership positions for at least 30 days.

(9) An employee accepting a position that requires membership shall become a member even if the employee previously declined membership under this section.

Optional membership – employees not in elected office