Any business in the service industry feels a certain amount of pressure to hire the most attractive employees to represent their public "face." While it might not seem fair to hire or reject people based on their attractiveness, it's not generally illegal. Being a plain Jane or Joe is not federally protected. What makes appearance standards illegal is when they are based on protected characteristics, such as age, race, and gender.
Take the "all-American" image. Does it evoke a picture of a blond-haired, blue-eyed individual? If so, you could find yourself face-to-face with charges of race discrimination. Abercrombie & Fitch was accused of hiring mostly white men to be "brand representatives"; those who didn't fit that look (i.e., ethnic minorities and women) were not hired or else were relegated to backroom jobs. The store ultimately agreed to settle claims of race and sex discrimination for $50 million.
Appearance standards not based on immutable characteristics associated with a protected characteristic will likely stand up in court. Harrah's Casino implemented a "Personal Best" program in order to improve the company's public image. All employees were required to "be well groomed, appealing to the eye, and be firm and body toned." Specifically, female employees were required to style their hair, wear makeup, and polish their nails. Male employees could not have long hair, wear makeup, or wear colored nail polish. A female bartender was fired for refusing to wear makeup, and she sued for sex discrimination. The full 9th Circuit Court of Appeals, generally considered employee-friendly, agreed with a panel of the 9th Circuit and with a district court and ruled against the female bartender.
The same reasoning would likely apply to the Borgata Hotel Casino & Spa's weight policy, which has drawn criticism for being biased against women. The casino started weighing its so-called "Borgata Babes" (cocktail servers) and bartenders for baseline numbers. Anyone who gains more than 7% of their body weight faces termination if they don't lose the weight within a 90-day unpaid suspension. Most of the employees affected are women, but they would be hard-pressed to assert a sex discrimination claim since male employees are held to the same standard.
Interestingly, the first legal shot was fired by a man. Weight discrimination claims don't stand much of a chance, either, though, unless morbid obesity or medical conditions are involved. And the Borgata is not located in one of the few areas that have appearance discrimination laws (e.g., Santa Cruz and San Francisco, CA; Michigan; Washington, DC).
In general, employers have the right to impose appearance standards, as long as:
there is a legitimate business need (e.g., maintaining the company's image);
it is not based on an immutable characteristic (e.g., skin color); and
employees are equally burdened.