1. The Treaty provision concerning the accession of new Member States contains only few conditions of a substantive nature. In particular, it does not regulate the extent to which modifications to the Treaty and thereby exceptions from the uniform application of Community law can be agreed upon on the occasion of an accession. From general principles one can, however, conclude that at an accession only such modifications are admissible which leave the identity of the Community untouched. Therefore, the fundamental principles of the Community, i.e. its institutional framework and the basic structural principles, must be preserved without change.
2. The principles of unity of law and non-discrimination between Member States and Union citizens demand the justification of transitional measures in every individual case. The adaptation difficulties that result from the accession of new Member States can serve as justification. In addition, a certain leeway for discretion exists. Exceptions from Community law caused by accessions need to fulfill a function of adaptation and security. This has been the case with the practice of the enlargements of the Community so far.
3. The possibility of justification of transitional measures leads to a variable system for the admissibility of provisions which have to distinguish a substantive and a time-related component. Exceptions are prohibited if they change those fundamental principles defining the identity of the Community. The less closely related they are to those fundamental principles, i.e. the less important the involved legal rules are for the identity of the Community, the easier they are to justify. Also, the possibilities of justifying an exception are greater if the exception only exists for a short time. Exceptions are not allowed permanently as far as they refer to fundamental Community law.
4. As it stands now, limits to the amendment of the Treaties are still disputable, and they are not subject to judicial review. A more differentiated approach could, at least, change this situation with regard to a distinction between modifications in substance and modifications within the accession process.