Can a GHP require a disabled retiree who is eligible for Medicare due to disability to enroll in Medicare as a condition to coverage? The GHP would pay secondary to Medicare.

We don't "require" our retirees under 65 who qualify for Medicare as disabled to enroll in Medicare BUT our plan pays secondary and will pay as if they were enrolled. That means if the retiree does not have Medicare, they will have a huge gap in coverage. For example, for an average hospitalization, Medicare will pay the entire amount less the deductible. Since out plan pays secondary as if the retiree had Medicare, our plan would only consider the deductible amount and pay accordingly.

My plan requires all retirees (including Long Term Disability Retirees) who are eligible for Medicare A free of charge, to enroll in Part B. If they choose not not enroll in part b we drop them from coverage. The key for us is "Eligible for Medicare A free of cost".