In the corporate "tolerance" film I watched (at Ernst & Young) a member of a protected class could not easily be fired - there would have to be a dossier constructed and all sorts of legal hoops to jump through to prevent civil lawsuits or government scrutiny.
The film explicitly stated that a heterosexual, Christian, white male was not protected and could be fired easily and with no legal complications.
That what I understand protected class to mean. I don't know anybody else's definition.
I am a Jew who has been fired. I have friends who are Jewish who have been fired. Seems we are not that well protected.