Early warning system
The Convention on the Future of Europe has proposed an "alarm bell" system.
This system allows national parliaments to object to a Commission proposal within six weeks of its publication on the grounds that it breaches the principle of subsidiarity. That is to say, breaching the principle that if something may be achieved better at a local level then the EU should not interfere. In this case, the "reasoned opinion" of one or several national parliaments has to be taken into account. Only if 1/3 of the national parliaments submit such a reasoned opinion would the Commission be required to review the proposal, but would not be obliged to alter or withdraw it.
Links
See EU Constitution, the Convention Working Group for Subsidiarity and the Protocol on the Application of the Principle of Subsidiarity and Proportionality in the EU Constitution.
