The paper analyzes the effect of proportionality in the field of constitutional institutional law, i.e. rules on structures and powers of government. It is grounded that this constitutional principle is primarily a limitation of possible arbitrariness of public authority. Therefore, it is argued that the principle of proportionality cannot have the same application here as in the constitutional rights of individuals. Exceptions can be made when the relevant person or institution are vested with public legal rights with the possibility of their constitutional adjudication.