In plain English it means that the EU should not get involved in matters which do not concern it.
The official version runs as follows:
“The Community shall act within the limits of the powers conferred on it by this Treaty and of the objectives assigned to it therein.
In areas which do not fall within its exclusive competence, the Community shall take action, in accordance with the principle of subsidiarity, only if and insofar as the objectives of the proposed action cannot be sufficiently achieved by the Member States and can therefore, by reason of the scale or effects of the proposed action, be better achieved by the Community.
Any action by the Community shall not go beyond what is necessary to achieve the objectives of the Treaty.”
What this means in practice is that the European Commission must justify the relevance of any proposals against the principle, and in fact, when proposals go to the European Parliament committees it is one of the first tests they consider.
If you feel that a proposal is just another example of over regulation, i.e. it is entirely disproportionate, then you may have strong grounds for opposing it on the grounds of proportionality.
Equally, if you believe that the issue being addressed by the legislation is not trans-european, and should therefore be addressed by individual Member States then again you might have grounds for opposition on the grounds of subsidiarity.
source: europeanlawmonitor.org
