SDCL § 58-18A-62: Prohibited grounds for reduction of benefits.

No COB provision may be used that permits a plan to reduce its benefits on the basis that:

(1) Another plan exists and the covered person did not enroll in that plan;

(2) A person is or could have been covered under another plan, except with respect to Part B of Medicare; or

(3) A person has elected an option under another plan providing a lower level of benefits than another option that could have been elected.