California Code, Business and Professions Code - BPC § 5054

(a) Notwithstanding any other provision of this chapter, an individual or firm holding a valid and current license, certificate, or permit to practice public accountancy from another state may prepare tax returns for natural persons who are California residents or estate tax returns for the estates of natural persons who were clients at the time of death without obtaining a permit to practice public accountancy issued by the board under this chapter or a practice privilege pursuant to Article 5.1 (commencing with Section 5096) provided that the individual or firm does not physically enter California to practice public accountancy pursuant to Section 5051, does not solicit California clients, and does not assert or imply that the individual or firm is licensed or registered to practice public accountancy in California.

(b) The board may, by regulation, limit the number of tax returns that may be prepared pursuant to subdivision (a).