One challenge faced by the Eastern European Union is

One of the many challenges faced by European Union is the departure of Britain (UK) from the European Union also known as Brexit.

Explanation:

European Union is a community in which the European countries have pledged their sovereignty and loyalty to the European community. They have made laws and regulations which they promptly follow.

The European Union consist of approximately 28 countries, mostly which are the countries which had participated in World war II and/or were communist.