In its 1993 Maastricht decision, the German Constitutional Court ruled that national authorities are not bound to respect and apply Community law to the extent that it exceeds the outer boundaries of Germany’s transfer of sovereignty to the E.U. The Court also ruled that no transfer of sovereignty is valid to the extent that it results in a violation of the fundamental individual rights guaranteed in the German Constitution. Nevertheless, a subsequent ruling on this subject indicated a willingness to rely on the European Court of Justice (ECJ) for the vindication of those fundamental rights.
The complete essay is at Essays on Two Federal Empires.