It ensures that decisions are taken as closely as possible to the citizen and that constant checks are made to verify that action at EU level is justified in light of the possibilities available at national, regional or local level. Specifically, it is the principle whereby the EU does not take action (except in the areas that fall within its exclusive competence), unless it is more effective than action taken at national, regional or local level. It is closely bound up with the principle of proportionality, which requires that any action by the EU should not go beyond what is necessary to achieve the objectives of the Treaties.
The Protocol on the application of the principles of subsidiarity and proportionality requires the principle of subsidiarity to be respected in all draft legislative acts and allows national parliaments to object to a proposal on the grounds that it breaches the principle, as a result of which the proposal may be maintained, amended or withdrawn by the Commission, or blocked by the European Parliament or the Council. In the case of a breach of the principle of subsidiarity, the Committee of the Regions may also refer
directly to the Court of Justice of the EU.