Non-retroactivity is one of the general principles of law. There is an open relationship between this principle and the principle of respect for vested rights. However, in some cases where there isn't any vested rights, the retrospectivity of laws are against the principle of equity. Hence special attention has been given to the principle of protection of legitimate expectations. There have been dissenting opinions between the High Court of Appeal and the Council of State on the matter of collecting the costs of illegal usage, dissipation, transmission, distribution, etc. in electricity bills from consumers. Thereupon, the legislator has made some amendments in the Electricity Market Law No. 6446. One of them constitutes the legal basis for the collection of the relevant fees and the other foresees the application of these amendments to pending cases. The Constitutional Court has judged that the regulation on apply these amendments to pending cases isn't unconstitutional.As a result, even though it is possible to agree with the judgement of the Constitutional Court, it should be added that the justification and the logical sequence followed are not satisfactory enough. Since the Court, in the process of transferring the principle of protection of legitimate expectations from the abstract level to the concrete level, could not clearly draw the framework in terms of scope and conditions, the Court's approach to this principle needs to be further explained and discussed.