California Code, Government Code - GOV § 1126

(a) Except as provided in Sections 1128 and 1129, a local agency officer or employee shall not engage in any employment, activity, or enterprise for compensation which is inconsistent, incompatible, in conflict with, or inimical to his or her duties as a local agency officer or employee or with the duties, functions, or responsibilities of his or her appointing power or the agency by which he or she is employed.  The officer or employee shall not perform any work, service, or counsel for compensation outside of his or her local agency employment where any part of his or her efforts will be subject to approval by any other officer, employee, board, or commission of his or her employing body, unless otherwise approved in the manner prescribed by subdivision (b).

(b) Each appointing power may determine, subject to approval of the local agency, and consistent with the provisions of Section 1128 where applicable, those outside activities which, for employees under its jurisdiction, are inconsistent with, incompatible to, or in conflict with their duties as local agency officers or employees.  An employee's outside employment, activity, or enterprise may be prohibited if it:  (1) involves the use for private gain or advantage of his or her local agency time, facilities, equipment and supplies;  or the badge, uniform, prestige, or influence of his or her local agency office or employment or, (2) involves receipt or acceptance by the officer or employee of any money or other consideration from anyone other than his or her local agency for the performance of an act which the officer or employee, if not performing such act, would be required or expected to render in the regular course or hours of his or her local agency employment or as a part of his or her duties as a local agency officer or employee or, (3) involves the performance of an act in other than his or her capacity as a local agency officer or employee which act may later be subject directly or indirectly to the control, inspection, review, audit, or enforcement of any other officer or employee or the agency by which he or she is employed, or (4) involves the time demands as would render performance of his or her duties as a local agency officer or employee less efficient.

(c) The local agency shall adopt rules governing the application of this section.  The rules shall include provision for notice to employees of the determination of prohibited activities, of disciplinary action to be taken against employees for engaging in prohibited activities, and for appeal by employees from such a determination and from its application to an employee.  Nothing in this section is intended to abridge or otherwise restrict the rights of public employees under Chapter 9.5 (commencing with Section 3201) of Title 1.

(d) The application of this section to determine what outside activities of employees are inconsistent with, incompatible with, or in conflict with their duties as local agency officers or employees may not be used as part of the determination of compensation in a collective bargaining agreement with public employees.