California Code, Business and Professions Code - BPC § 851

(a) There is direct statutory authority or requirement that the board or examining committee utilize the standards of the specified private voluntary association or professional society; or

(b) The board or examining committee specifies in the regulation the amount of education, training, experience, examinations, or other requirements of the private voluntary association or professional society, which standards shall be consistent with the provisions of law regulating such licensees, and the board or examining committee adopts such standards in public hearing. The board or examining committee may, by regulation, require an applicant to successfully complete an examination conducted by or created by a relevant national certification association, testing firm, private voluntary association, or professional society.

Nothing in this section authorizes the Medical Board of California to limit the licensure of physicians and surgeons by specialty.