Union law is divided into 'primary' and 'secondary' law. Primary law refers in particular to the Treaties that are the basis for all EU action.
Secondary law is derived from the principles and objectives set out in the Treaties and includes regulations, directives and decisions.
Member States have primary responsibility for the correct and timely application of EU Treaties and legislation, and the Commission monitors the application of Union law.
The Commission may take action if a Member State:
If no solution can be found at an early stage, the Commission can open formal infringement proceedings and eventually refer the Member State to the European Court of Justice.