Mont. Code Ann. § 90-6-323

A local government unit may budget and expend payments received from a mineral developer under this part or part 4 of this chapter or pursuant to a plan approved under this part. If a payment is requested or received after the adoption of the budget for the fiscal year in which the payment is to be expended, the governing body of the local government unit may by a majority vote amend its budget to provide for the receipt and expenditure of the payment.