Montana Code Ann-Title 33-Chapter 1-Part 1. General Provisions
Prohibition on retroactive denial.
Retroactive Denial
When prior authorization for a covered service is required of and obtained by or on behalf of a member, the approval is final and may not be rescinded after the covered service has been provided. This section does not apply to cases of fraud, misrepresentation, nonpayment of premium, and exhaustion of benefits or if the member for whom the prior approval was granted is not covered when the service is provided.