Mont. Code Ann. § 19-3-412

(1) elected officials of Except as provided in subsection (2), the state or local governments who following employees in covered positions that are paid on a salary or wage basis rather than on a per diem or other not elected offices shall elect either to become active members of the retirement system or reimbursement basis; to decline this optional membership by filing an irrevocable, written application with the board in the manner prescribed in subsection (3):

(a) employees serving in employment that does not cumulatively exceed a total of 960 hours of covered employment with all employers under this chapter in any fiscal year;

(b) employees directly appointed by the governor;

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

(d) the chief administrative officer of any city or county; and

(e) employees of county hospitals or rest homes.

(2) part-time employees serving in employment that does not exceed the equivalent of 120 working days in any fiscal year;

(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) employees directly appointed by the governor;

(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) employees working 6 months or less for the legislative branch Failure to perform work related to the legislative session; 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 chief administrative officer of any city or county; 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) employees of county hospitals or rest homes Except as provided in the sixth- and seventh-class counties. 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

The following employees in covered employment may become members of the retirement system at their option at any time during their employment in a covered position by filing a membership card with the board: