[JimRed]

It really should be legal to identify political affiliation as a job requirement.

Where (under what law or regulation) is it forbidden?

[SgtHooper]

For the rats, it might be construed under the Americans with Disabilities Act (ADA)! :-) You raise a good point, but my intuition thinks there might be some trouble with asking a candidate employee their political affiliation. Not sure how though.