Gov. Code, § 3521

(a) In determining an appropriate unit, the board shall be governed by the criteria in subdivision (b). However, the board shall not direct an election in a unit unless one or more of the employee organizations involved in the proceeding is seeking or agrees to an election in such a unit.

(b) In determining an appropriate unit, the board shall take into consideration all of the following criteria:

(1) The internal and occupational community of interest among the employees, including, but not limited to, the extent to which they perform functionally related services or work toward established common goals; the history of employee representation in state government and in similar employment; the extent to which the employees have common skills, working conditions, job duties, or similar educational or training requirements; and the extent to which the employees have common supervision.

(2) The effect that the projected unit will have on the meet and confer relationships, emphasizing the availability and authority of employer representatives to deal effectively with employee organizations representing the unit, and taking into account such factors as work location, the numerical size of the unit, the relationship of the unit to organizational patterns of the state government, and the effect on the existing classification structure or existing classification schematic of dividing a single class or single classification schematic among two or more units.

(3) The effect of the proposed unit on efficient operations of the employer and the compatibility of the unit with the responsibility of state government and its employees to serve the public.

(4) The number of employees and classifications in a proposed unit and its effect on the operations of the employer, on the objectives of providing the employees the right to effective representation, and on the meet and confer relationship.

(5) The impact on the meet and confer relationship created by fragmentation of employees or any proliferation of units among the employees of the employer.

(6) Notwithstanding the foregoing provisions of this section, or any other provision of law, an appropriate group of skilled crafts employees shall have the right to be a separate unit of representation based upon occupation. Skilled crafts employees shall include, but not necessarily be limited to, employment categories such as carpenters, plumbers, electricians, painters, and operating engineers.

(c) There shall be a presumption that professional employees and nonprofessional employees should not be included in the same unit. However, the presumption shall be rebuttable, depending upon what the evidence pertinent to the citeria set forth in subdivision (b) establishes.