Cal. Penal Code § 626.7
(a) If a person who is not a student, officer, or employee of a public school, and who is not required by his or her employment to be on the campus or any other facility owned, operated, or controlled by the governing board of that school, enters a campus or facility outside of the common areas where public business is conducted, and it reasonably appears to the chief administrative officer of the campus or facility, or to an officer or employee designated by the chief administrative officer to maintain order on the campus or facility, that the person is committing any act likely to interfere with the peaceful conduct of the activities of the campus or facility, or has entered the campus or facility for the purpose of committing any such act, the chief administrative officer or his or her designee may direct the person to leave the campus or facility. If that person fails to do so or if the person returns without following the posted requirements to contact the administrative offices of the campus, he or she is guilty of a misdemeanor and shall be punished as follows:
(3) If the defendant has been previously convicted two or more times of a violation of any offense defined in this chapter or Section 415.5, by imprisonment in a county jail for a period of not less than 90 days or more than six months, or by both that imprisonment and a fine of not more than five hundred dollars ($500), and the defendant shall not be released on probation, parole, or any other basis until he or she has served not less than 90 days.
For purposes of this section, a representative of a school employee organization engaged in activities related to representation, as provided for in Chapter 10.7 (commencing with Section 3540) of Division 4 of Title 1 of the Government Code, shall be deemed a person required by his or her employment to be in a school building or on the grounds of a school.