According to the New York Times, European Union's highest court released an advisory opinion stating that companies can ban employees from wearing religious garb in the workplace if they have a policy in place that applies to all religious garb equally.
However, this doesn't mean that all companies can prohibit employees from wearing religious garb and that many bans are often religious discrimination. There are many factors that an employer must consider including but not limited to the type of work the employee does and the size of the religious symbol (a small cross or a large print?).
This advisory opinion was issued after a Muslim woman in Belgium sued the company she worked at after they denied her request to be able to wear a head scarf at work. A formal judgment on the matter is still pending for later in the year, however, the opinion usually gives a people an idea of what to expect.
The United States is familiar with cases of religious men and women wanting to wear religious garb in different types of work. The New York Times uses the example of an Orthodox Jewish Coast Guard recruit who wanted to wear a skullcap on duty.