The principle of legality means in administrative law legal guidance, which requires that the functioning of public administration as public authority is bound by the statutes and legal norms and principles, which have in the legal system position and power of the statute, which are as valid legal basis applicable for administrative operation, so that it does not conflict with the law (i.e. the priority of the law) and is based on the relevant statutory authorization (i.e. the reservation of the law). In relation to its effects, the result of the application of the principle of legality shall be in simultaneous restriction and authorizing of administration. The principle of legality is a central component of (the state governed by) the rule of law.
Unlike the notion of legality, the principle of legality as a legal principle reflects in different intensities in the operation of administration, while the certain administrative act can be either legal or illegal, without any intermediate steps. The principle of legality therefore explains and outlines how the administration is legally bound while legality stems from these findings and is grounded upon them.
Special feature of the principle of legality in administrative law is the reservation of the law, which has also an important steering function for the operation of administration. The concept of the reservation of the law primarily relates to the question of the existence of the relevant authorization for the administration, but it also necessarily comprises the criteria and other legal principles that shall be followed in the use of these authorizations; an example is a fundamental requirement of clarity and certainty of the legislation (lex certa). As a component of the principle of legality the priority of the law and the reservation of the law are both applicable to all administrative acts, i.e. when administration acts ex iure imperii. In case of intervention administration where encroachment on fundamental rights occurs, the criteria for admissibility of the administrative operation is the most rigorous so the explicit statutory authorization is required. In service administration with incentive character and orientation in improvement of the standard of living, general and less precise authorization may be sufficient.
In the functioning of the administration through private acts – ex iure gestionis, the reservation of the law as a component of the principle of legality is not effective. However, this does not mean that only for this reason the administration is less legally bounded in such cases, because it must follow the law and of course the constitution, which guarantees individuals fundamental rights and freedoms in relation to the state.
Exceptionally, the principle of legality indirectly extends even to relationships between private-law entities. I name this horizontal effect of the principle of legality. This can typically occur in situations where the administration governs relations between entities in the field of private law. Unique evidence of the existence of the horizontal effect of the principle of legality is certain effectiveness of human rights and fundamental freedoms between individuals.
The principle of legality is implemented in a variety of forms of administrative operation in a modern state. The standards of the principle of legality, particularly those relating to the reservation of the law, are not universal and rigid but adaptable to social development and functioning of the state organization. According to my findings, this cannot be taken as a conceptual defect of the principle of legality, rather the opposite – its advantage, as the administrative law is generally known for its relatively fast changes. This should correspondingly affect the concept of the principle of legality. Moreover, while its intensity may vary, the principle of legality is finally applied in a concrete assessment of whether a certain act of administration is legal or illegal and this decision is made by the competent authority on the basis and within the rules of the prescribed proceeding.