Bus. & Prof. Code, § 7059

(a) The board may adopt reasonably necessary rules and regulations to effect the classification of contractors in a manner consistent with established usage and procedure as found in the construction business, and may limit the field and scope of the operations of a licensed contractor to those in which they are classified and qualified to engage, as defined by Sections 7055, 7056, 7057, and 7058. A licensee may make application for classification and be classified in more than one classification if the licensee meets the qualifications prescribed by the board for such additional classification or classifications. The application shall be in a form as prescribed by the registrar and shall be accompanied by the application fee fixed by this chapter. No license fee shall be charged for an additional classification or classifications.

Nothing contained in this section shall prohibit a specialty contractor from taking and executing a contract involving the use of two or more crafts or trades, if the performance of the work in the crafts or trades, other than in which they are licensed, is incidental and supplemental to the performance of the work in the craft for which the specialty contractor is licensed.

(b) (1) In public works contracts, as defined in Section 1101 of the Public Contract Code, the awarding authority shall determine the license classification necessary to bid and perform the project, in accordance with the classifications prescribed by this article and as set forth in Division 8 of Title 16 of the California Code of Regulations. In no case shall the awarding authority award a prime contract to a specialty contractor whose classification constitutes less than a majority of the project. When a specialty contractor is authorized to bid a project, all work to be performed outside of their license specialty, except work authorized by subdivision (a), shall be performed by a licensed subcontractor in compliance with the Subletting and Subcontracting Fair Practices Act (Chapter 4 (commencing with Section 4100) of Part 1 of Division 2 of the Public Contract Code).

(2) Nothing contained in this subdivision shall be construed as authorizing an awarding authority to enact regulations relating to the qualifications necessary to engage in the business of contracting.

(3) Nothing contained in this subdivision shall deprive the registrar of the authority to investigate complaints and commence disciplinary proceedings for violations of this chapter.