Enrollment Reshaping Entry For Older, Retiring Members Act or the Enrollment REFORM Act This bill establishes and otherwise modifies requirements relating to coordinated coverage between employer health insurance and Medicare. Specifically, the bill prohibits employer-sponsored health plans for certain smaller employers from reducing benefits for employees who are eligible for Medicare but have not yet enrolled. Additionally, for purposes of calculating the Medicare late enrollment penalty, an individual seeking to demonstrate proof of enrollment in an employer-sponsored health plan may not be required to provide proof for more than the immediately preceding 36-month period, with specified exceptions.