IANAL, but as I understand it, the typical qualifiers for being a protected class tend to be immutable (sex, race, age, disability, color, creed, national origin, religion, or genetic information, per Wikipedia[0].) Obviously you can change your sex and religion, though, and disability status in some cases, though.

Maybe a case could be made for political affiliation under "creed," since there appears to be no specific legal definition for that[1], although the consensus seems to be centered around religious belief.

In any case, since one can (and many people do) change their political affiliations often, I would expect such a law to meet with some extreme legal challenges at the very least, because it seems like such an obvious attempt to game the system, particularly since "discrimination against a political group" is pretty much the purpose of other political groups.

[0]https://en.wikipedia.org/wiki/Protected_group

[1]https://law.stackexchange.com/questions/8686/what-is-a-creed...