The short answer to the question, “Am I required to get Medicare Supplemental Insurance”, is no. However, that is not the whole story.
Medicare is a government run health insurance program for U.S. citizens aged 65 and older. Payment rates for hospital, doctor, and diagnostic services are set by the government, and in most cases, do not fully cover all the expenses they bill. If a provider, such as a doctor, does not accept Medicare assignment, then he or she will receive no money from Medicare. The bill will be sent to Medicare and Medicare will send a check directly to you. You will have to pay the provider. When this happens you will quickly learn that Medicare does not pay all the charges billed by the provider. Medicare only pays about 80% of the total, and the remaining 20% will come out of your pocket. A $5,000 hospital stay would cost you $1,000. A Medicare Supplemental Insurance policy would cover all, or most all, of the $1,000 Medicare did not pay. Even providers who accept Medicare assignment do not get paid the total amount they bill. If they accept assignment, they cannot bill you for the remainder. However, if you have a supplemental policy, it will pay a portion of what Medicare does not and your provider will be much happier with you for it.
No, there is no law or rule that says you have to have a Medicare Supplemental Insurance policy. No one will make you buy one. However, one could save you a lot of money.