That is simply not true (in California). If the underlying lawsuit is based on employment Discrimination or Harassment under the California Fair Employment and Housing Act, firing the employee because they filed the lawsuit itself subjects the company to liability. It's called a "Tameny Claim" -- a "Discharge in Violation of Public Policy." [1]
Of course, proving that the reason for the firing was Retaliation isn't easy, but that doesn't make your statement true.
Of course, proving that the reason for the firing was Retaliation isn't easy, but that doesn't make your statement true.
[1] https://scholar.google.com/scholar_case?q=tameny+v+atlantic+...