Cal. Pub. Cont. Code § 20118.4

(a) If any change or alteration of a contract governed by Article 3 (commencing with Section 17595) of Chapter 5 of Part 10.5 of the Education Code is ordered by the governing board of the district, the change or alteration shall be specified in writing and the cost agreed upon between the governing board and the contractor. The board may authorize the contractor to proceed with performance of the change or alteration, without the formality of securing bids, if the cost so agreed upon does not exceed the greater of the following:
1. (1) The amount specified in Section 20111 or 20114, whichever is applicable to the original contract.
2. (2) Ten percent of the original contract price.
(b) The governing board of any school district, or of two or more school districts governed by governing boards of identical personnel, having an average daily attendance of 400,000 or more as shown by the annual report of the county superintendent of schools for the preceding year, may also authorize any change or alteration of a contract for reconstruction or rehabilitation work, other than for the construction of new buildings or other new structures, if the cost of the change or alteration is in excess of the limitations in paragraphs (1) and (2) of subdivision (a) but does not exceed 25 percent of the original contract price, without the formality of securing bids, and the change or alteration is a necessary and integral part of the work under the contract and the taking of bids would delay the completion of the contract. Changes exceeding 15 percent of the original contract price shall be approved by an affirmative vote of not less than 75 percent of the members of the governing board.