A protected class is a group that is illegal to discriminate against in this manner, in the United States (and several other legal systems).
"Phone OS" is not a protected class. Many other things are, though, such as Race, Religion, Sex, etc... Varying a bit by jurisdiction and legal system.
Edit: Seems like I misunderstood the parent usage of class to refer to the terms as a sociological term not as its US legal term. Sorry about that