Mont. Code Ann. § 5-7-210

Whenever a lobbyist invites a legislator to attend a function that the lobbyist or the lobbyist's principal has fully or partially funded or sponsored or whenever a lobbyist offers a legislator a gift, the lobbyist shall, upon request, supply the recipient legislator with the benefit's true or estimated cost and allow the legislator to reimburse. The expenditures must be itemized in the principal's reports with a notation "reimbursed by benefactee".