California Code, Business and Professions Code - BPC § 16100

(a) The board of supervisors may in the exercise of its police powers, and for the purpose of regulation, as herein provided, and not otherwise, license any kind of business not prohibited by law, transacted and carried on within the limits of its jurisdiction, including all shows, exhibitions, and lawful games, and may fix the rate of the license fee and provide for its collection by suit or otherwise.

(b) No license fee levied pursuant to subdivision (a) that is measured by the licensee's income or gross receipts, whether levied by a charter or general law county, shall apply to any nonprofit organization that is exempted from taxes by Chapter 4 (commencing with Section 23701) of Part 11 of Division 2 of the Revenue and Taxation Code or Subchapter F (commencing with Section 501) of Chapter 1 of Subtitle A of the Internal Revenue Code of 1986,  1 or the successor of either, or to any minister, clergyman, Christian Science practitioner, rabbi, or priest of any religious organization that has been granted an exemption from federal income tax by the United States Commissioner of Internal Revenue as an organization described in Section 501(c)(3) of the Internal Revenue Code or a successor to that section.

(c) Before a county issues a business license to a person to conduct business as a contractor, as defined by Section 7026, the county shall verify that the person is licensed by the Contractors State License Board.