coffeemug

I am insured through my company and I chose to opt-out my family members since the rate would be too high to insure them. My question is if my insurance company can specifically require that I provide them with proof of insurance (company name, group, and group/id numbers)? Currently my HR manager is asking for this information and I don't wish to provide it. Is this legal that it be required information? I live in California if that has any weight on the matter.