If you have coverage through an employer or union group health plan and want to enroll in Medicare Part B, you should carefully consider your options and the potential costs and benefits of each coverage. If your employer or union group health plan is considered primary to Medicare, you should delay enrolling in Medicare Part B until your employment or union coverage ends. If Medicare is considered primary, you should enroll in Medicare Part B during your Initial Enrollment Period to avoid late enrollment penalties. You may also be able to use a Special Enrollment Period to enroll in Medicare Part B if you lose your employer or union coverage or if your employer or union stops offering coverage. It is recommended that you consult with a healthcare professional or insurance advisor to help you make an informed decision.