Mont. Code Ann. § 69-4-351

The public utility shall have the duty to maintain, repair, and replace all underground facilities installed pursuant to this part. There shall be no competitive bidding as to the construction of the converted facilities since existing facilities are owned, maintained, and operated by the public utility and the continuity of service of the utility is essential, both of which make construction work by third persons impracticable. Therefore, the public utility concerned shall be responsible for the accomplishment of all construction work and may contract out such of the construction work as it deems desirable.