Section 20136 Of Article 3.5. Counties From California Public Contract Code >> Division 2. >> Part 3. >> Chapter 1. >> Article 3.5.

. Whenever the board enters into a contract for the erection, construction, alteration, or repair of any public building or other structure, the contract shall not be altered or changed in any manner, except:
  (a) As provided in Section 20142.
  (b) As provided for in the contract itself, or specifications.
  (c) By order adopted by a vote of two-thirds of the board, and the consent of the contractor.