I recently had surgery that resulted in removing cancer. I have a supplemental insurance plan paid for solely by me that will cover reimbursements (ie. Aflac). My employer is requesting copies of my claim submissions, which includes private healthcare information, for my "file". Can they do this? If not, how could this be addressed and dealt with?

Did you purchase this supplemental through your company? Why are they asking for this, what is their reasoning?

This is not a HIPAA violation - HIPAA deals with health care professionals who inappropriately share medical information with others. Your employer requesting information from you is not a violation. Your real question is whether you are obligated to provide information to your employer about your health insurance policy that you pay for on your own. I assume you took significant time off from work, and perhaps you were on disability pay? They are probably looking for proof that you were on medical leave, and the insurance explanation of benefits is one way to do that. Otherwise you were AWOL and they may have had you terminated. So I suggest you ask why they are looking for this info, and if it's for the reason above then I would suggest that you comply.