Mont. Code Ann. § 30-11-302

Any merchant has the right to request any individual on the merchant's premises to place or keep in full view any merchandise that the individual may have removed, or that the merchant has reason to believe the individual may have removed, from its place of display or elsewhere, whether for examination, purchase, or for any other purpose. A merchant may not be criminally or civilly liable for slander, false arrest, or otherwise on account of having made such a request.