Workplaces have become more relaxed in recent decades when it comes to what kind of clothing employees are allowed or required to wear. Gone are the Mad Men days where men wore suits and ties, and women wore dresses and skirts. Casual Fridays have given way to full-time casual dress in many offices where employees aren't regularly dealing with the public or clients.
Employers have a right to implement and enforce a dress code that they believe is appropriate for their workplace. However, they need to be careful that their requirements can't be viewed as discriminatory. In some cases, they might even be illegal.