Cal. Education Code § 45045

When a school district operates on a year-round schedule pursuant to Chapter 5 (commencing with Section 37600) of Part 22 of this division, the salary of an employee who is employed for the extended school year and who previously had been assigned to a 9- or 10-month teaching position in the same district shall be adjusted in accordance with the ratio of the extension in the number of days expected to be taught by said employee to the number of days expected to be taught by employees in the district in the school year prior to the commencement of year-round operation. A full-time probationary or permanent classroom teacher currently employed by a school district which converts to a continuous school program shall not, without his written consent, be required to teach under such program more than 180 days during a school year, or more than the number of days the schools of the district were maintained during the year preceding implementation of the continuous school program, whichever is the greater. This section shall not be construed as limiting the power of school district governing boards to govern the schools of the district, including the assignment of teachers employed by the district.