According to the EEOC, "A dress code must not treat some employees less favorably because of their national origin. For example, a dress code that prohibits certain kinds of ethnic dress, such as traditional African or Indian attire, but otherwise permits casual dress would treat some employees less favorably because of their national origin.
An employer may require all workers to follow a uniform dress code even if the dress code conflicts with some workers' ethnic beliefs or practices. However, if the dress code conflicts with religious practices, the employer must modify the dress code unless doing so would result in undue hardship."