An insurer, health service corporation, or health maintenance organization may not place an elimination rider on or rescind coverage provided by a disability policy, certificate, or subscriber contract after a policy, certificate, or contract has been issued unless the insured has made a material misrepresentation or fraudulent misstatement on the application or has failed to pay the premium when due.
Postclaim Underwriting Prohibited -- Condition
Mont. Code Ann. § 33-18-215, under Insurer's Relations With Insured and Claimant.
Mont. Code Ann. § 33-18-215