Mont. Code Ann. § 18-1-304

Any amount deducted by the state of Montana or by any department, agency, or political subdivision thereof pursuant to the terms of a contract from the retained payments otherwise due to the contractor thereunder shall be deducted first from that portion of the retained payments for which no obligation has been substituted, then from the proceeds of any deposited obligation. In the latter case, the contractor shall be entitled to receive the interest, coupons, or income only from those obligations which remain on deposit after such amount has been deducted.