The procedural legitimacy of the ECB gained essential elements of its manifestation during the global economic and financial crisis, which in practice coincided with the adoption of new institutional models of macroeconomic management aimed at strengthening the entire economic system of the member countries. Until the outbreak of the debt crisis, the procedural identification of the ECB had a more sporadic character and was limited to the consequences of inadequate macroeconomic dialogue with other community institutions, primarily with the European Commission. With the adoption of new institutional mechanisms comes a significant redefinition of the basic principles of European monetary law (primarily in the area of the reach of the lex monetae in monetary traffic, extraterritorial application of monetary sovereignty, and non-compliance with the provisions on collective responsibility for public debt, i.e. a different view of the content of the lex contractus principle), which caused far-reaching monetary disputes. By analyzing these cases from court practice, we can see the best confirmation of the institutional, functional, and financial independence of the supreme monetary institution of the EU and from the outcome of the disputes identify its indisputable authority in shaping and derogating the norms of monetary law, where monetary stability appears as a conditio sine qua non of the economic stability of the entire eurozone.

The contribution of states in the implementation of the aforementioned principle can differ from one another depending on the level of development of monetary awareness, as well as solutions in positive monetary legislation, which must be regulated by special monetary legal regulations outside the branch of private (civil law), which normally happened in the period when monetary integration they were not so pronounced. Monetary legal regulations represent sui generis legal sources, whose object of social protection as a specific legal subject is determined by the need for optimal regulation, management, and protection of relations in which monetary agents (public legal entities) participate.

An important case from judicial practice is related to the consideration of the compatibility of the ECB program for the purchase of bonds on the secondary financial market (eng. outright monetary transaction-omt in the following text) with the primary law of the EU (founding acts). The ECB adopted this program in 2012 when the ESCB was authorized to purchase bonds on the secondary market to prevent the disruption of the normal flow of bond purchase transmission mechanisms and to preserve the single monetary policy. Namely, the ECB has previously established that bond interest rates in different member states are quite different from each other, where such differences in the level of rates do not arise from different macroeconomic conditions in specific states but are caused by a high demand for high-risk bonds that can bring the holder a significant premium. Transmission mechanisms show that with the policy of required reserves, the central bank determines the level of liquidity of commercial banks, where the client's expectations about the interest rate affect long-term (market) interest rates, so disturbances in its level affect the supply and demand for goods and services and determine their price. Such circumstances can affect the fragmentation of the banking market, and deviation from the generally accepted principles regarding debt refinancing conditions and credit costs in the eurozone, which reduces the contribution of monetary measures and instruments to the desired economic development and stability. The implementation of the concept of the mentioned measures in Germany, as a leading member of the Eurozone, was conditioned by the previous decision of the Constitutional Court on the legal nature of the mentioned concept, where the question arose as to whether the ECB has the mandate to adopt such a program following the provisions of primary law (due to the violation of Article 136 of the Treaty on EU on the prohibition of collective responsibility for public debt, i.e. the financing of other people's debts) and whether such actions call into question the basic principles of a democratic society guaranteed by the constitution. In its decision, the Constitutional Court took the view that the OMT program represents a form of arbitration by the ECB and that the consequences of debt crises, which can be expected in the future, do not give the ECB legitimacy to deviate from the principles established by the provisions of the founding acts. The lack of legitimacy of the OMT concept, according to the understanding of the German Constitutional Court, stems from the absence of quantitative restrictions when buying bonds, which can change the scope of financial support measures established by the Agreement on the European Stabilization Mechanism.

The European Court of Justice in its decision confirmed the legitimacy and legality of the ECB's proposed measures, justifying it by the fact that the OMT program falls under the sphere of the unified monetary policy that the ECB sovereignly conducts under the monetary strategy to preserve monetary stability, more precisely price stability as a primary goal that is more consistently realized through the application of the mentioned measures.3 In this context, in the court's decision we can see a clear distinction between the monetary and economic union in the EMU, which is precisely characterized by a strong monetary union and a weak (non-unified) economic policy. The OMT concept is de facto a measure of a unified monetary policy, which is conducted at the supranational level and whose goal is monetary stability, and not a measure of decentralized general economic policy, which the members conduct at the national level per the limitations of the principles of proportionality and subsidiarity, although we can note that these measures have an indirect effect on the general economic policy. When regarding the purchase of bonds on the secondary market, the Court considered that this does not violate the norms of primary law, but is simply a manifestation of one of the standard measures of the ECB established by its Statute (Article 18) and Protocol no. 4, which more precisely regulates the operations of the ECB on the open market. The implementation of the OMT program is conditioned by the tasks that the eurozone member states undertook during the ratification of the Agreement on the European Stabilization Mechanism, and it concerns the creation of macroeconomic adjustment programs, which once again confirms the impact of the measures on the goals of the general economic policy, but again, we emphasize only as secondary effects without danger to the violation of the principles of community law.

The ECJ was also of the opinion that the adopted measures do not violate the principle of proportionality, because the mentioned concept does not go beyond the necessary minimum to achieve monetary stability, which means that the goals are clearly defined within the framework of the program without an extensive interpretation of their purpose and justification. In connection with the potential ban on the violation of collective responsibility for the public debt (eng. no-bailout clause), the Court, similarly as when resolving the legal nature of the Fiscal Agreement, took the view that the mentioned clause prohibits any form of monetization of the state debt, i.e. of granting loans to the governments of member states by the ESCB as a lender, but does not fundamentally prohibit the ESCB from buying bonds from creditor states (which have previously come forward as issuers of those bonds). According to the Court's understanding, interventions by the ECB on the secondary market can in practice have the same effect as the purchase of securities on the primary financial market, if potential buyers of those bonds reliably know that the ECB is buying bonds under conditions that allow them to act as de facto intermediaries of the bank in transactions with public administration bodies of member states. In this sense, the Court's decision not only confirmed the independence of the ECB in its work but at the same time sent an unequivocal signal to all members of the Union that they cannot arbitrarily determine which community acts they will accept in national law because the implementation of community acts is the general interest of all member states. This action of the Court is particularly significant when taking into account earlier failures and decisions related to non-compliance with fiscal rules from the provisions of the Growth Stability Pact (the case of France and Germany), which the Court justified with its claims. Due to the specific nature of the relationship and outcome, monetary disputes cannot be conducted following the interests of politically influential member countries and justified by reasons of political pragmatism, but must primarily be motivated by the protection of institutions that perform their tasks in the interest of society and the economy in the manner de lege artis, which is, in our opinion, received its confirmation for the first time precisely in the case of the application of the OMT program. We can note that in monetary disputes, the request for constitutionality and legality assessment suffers from certain limitations, which was also confirmed by the European Court of Justice in its decision in the case of legal compliance with the ECB's measures on the purchase of bonds on the secondary market. It is clear from the Court's decision that conducting monetary policy requires the possession of professional knowledge and expertise, which in European monetary law only the ECB has and enjoys discretionary powers for its implementation. Given that in monetary disputes, the Court cannot interfere with the essence of monetary measures (because it has no competence for such a thing, the decision in most cases comes down to the application of the criteria of responsible behavior, i.e., the legal standards of a good businessman, who acts with due care when applying a certain monetary measure). Certainly, judges must acquire special knowledge in the field of monetary policy due to disputes that can be expected in the future, especially when the concept of the banking union takes root in its full sense. Although for some authors the decision of the ECJ on the OMT program represents another confirmation of the tendency to expand the competence of community institutions through the provisions of secondary legislation, we believe that in this particular case the behavior of the ECB was not contrary to the provisions of primary law, but only represents a new way of manifesting its competence in crisis conditions aimed at preserving assets of the EMU. Such action is following the principle of proportionality and is determined by the monetary targets, which in a broader view are in the function of achieving sustainable economic development, and where the fear of not knowing the goals of the monetary policy can be replaced by strengthening the macroeconomic dialogue between the ECB and the ECJ with wider participation of national central banks.