No. A person does not have to be an American citizen to file a discrimination lawsuit. The law protects everyone who has been a victim of discrimination, regardless of whether they are an American citizen. Also, nobody can question you about your citizenship status during the lawsuit since it is not a relevant topic. Moreover, a lawyer could actually risk losing his license or being reprimanded by the California State Bar (the organization that polices lawyers) if the lawyer threatened to report a non-American citizen to Immigration in retaliation for you filing a lawsuit. In sum, your citizenship status cannot be raised during the course of the lawsuit.