Nothing in this part shall prohibit any individual employed as a supervisor from becoming or remaining a member of a labor organization, but no employer subject to this part shall be compelled to deem individuals defined herein as supervisors as employees for the purpose of any law, either national or local, relating to collective bargaining.
Source:
Section 1166.2, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=LAB§ionNum=1166.2..