Cal. Gov. Code § 3571.3

The expression of any views, arguments, or opinions, or the dissemination thereof, whether in written, printed, graphic, or visual form, shall not constitute, or be evidence of, an unfair labor practice under any provision of this chapter, unless such expression contains a threat of reprisal, force, or promise of benefit; provided, however, that the employer shall not express a preference for one employee organization over another employee organization.