Mont. Code Ann. § 37-43-401

No action or counterclaim shall be maintained by any water well contractor, water well driller, or monitoring well constructor in any court in this state with respect to any agreement, work, labor, or materials for which a license is required by this chapter or to recover the agreed price or any compensation under any such agreement or for any such work, labor, or materials for which a license is required by this chapter without alleging and proving that such water well contractor, water well driller, or monitoring well constructor had a valid license at the time of making such agreement and of supplying such labor, work, or materials.