Having read through all the comments I am amazed at how behind employment law looks to me as an outsider from the other side of the 'pond'
Keep in mind that American business is based on a strong sense of property rights. The owner of a business has the right to mostly run his business how he sees fit. Except for well defined legal protections (like race, gender, etc.), employers can and should be allowed to hire and fire people based on how they want their business to be represented.

I don't want this to turn political, but you should understand that American business is very different than most of Europe, where "workers' parties" seem to dominate. Here, it's mostly an "open shop" environment except for certain trades (and only in certain areas) where labor unions are strong. Americans as a whole tend to favor the idea that employers should be free to run their business as they see fit, and if they turn out to be poor employers, people won't want to work for them. The good employers will retain good employees and the bad ones won't. The free market corrects itself. Employees therefore don't have any legal protection for wearing kilts to work, wearing green mohawks, or getting facial tattoos if the employer doesn't like it. The employer has every right to determine a dress code because it's his business. He owns it, not the employee. I fail to see how that's "behind" in any way.