Disclaimer, I am not a lawyer:

California labor law prevents employers from firing you for engaging in "protected activity" [0][1], which includes labor organizing and forms of political speech. They can still fire you for a long list of other reasons, though.

[0] https://www.dir.ca.gov/dlse/Glossary.asp?Button1=P

[1] https://www.shouselaw.com/ca/labor/harassment/political-reta...