I recently came across a law review article arguing that looks-based employment discrimination should be banned along with race-, age-, sex-, and disability-based discrimination. It pointed out that one's level of attractiveness is, like these other categories, largely immutable. It cited many studies suggesting that looks-based discrimination has a huge effect on hiring, promotions, and earnings--in some cases greater than the effect of race-based discrimination.
Of course, if looks are important to your job (model, maybe receptionist, etc.) the discrimination would be ok (just as blind people can't sue when they are denied positions as busdrivers.) But for most jobs, looks aren't really important.