31 CFR §8.28

1. (a)Attorneys, certified public accountants. The enrollment of a practitioner to whom an enrollment card has been issued will terminate when that person becomes eligible to practice without enrollment under § 8.2 (a) or (b), and that person shall surrender his or her enrollment card to the Director for cancellation.
2. (b)Expiration of enrollment. The enrollment of any person will automatically terminate after the date indicated on the enrollment card unless, during the 12-month period prior to the expiration date, that person applies for renewal of enrollment with the Director as provided in § 8.25. In this case, the person may continue to practice before the Bureau until his or her application has been finally determined.