When speaking of competition in the market for electronic communications in Croatia, an important role in ensuring and promoting efficient competition is played by HAKOM and AZTN. In this regard, on the one hand we have the activity of AZTN, which through application of ZZTN regulates general issues of market competition in Croatia, with particular emphasis on prevention and sanctioning of cartel behaviour. On the other hand, by applying ZEK, HAKOM in its capacity of sectoral regulator supervises the daily operation of undertakings in the telecommunications sector. In particular, it is one of HAKOM's primary duties to ensure equal terms for all operators active in the market for electronic communications. Operators of electronic communications must behave independently in their business activities. The agreements between undertakings who are mutual market competitors (i.e. who operate on the same production or distribution level) for the purpose of avoiding market competition between competitors and with the aim of (typically) increasing prices in order to achieve extra profit, are prohibited as they directly harm consumers, as well as the economy as a whole. The cartel participants usually agree on the prices of a product, share markets or allocate customers or locations for sale of their products or services, agree on discounts or collude on the terms to be put in public procurement bids, or close the market for new competitors (or for expansion of current ones) in some other way. These types of agreement are prohibited and in the practice subject to the most severe monetary penalties, which is why it is of essential importance for the undertakings to be familiar with the obligations, but also with rights arising out of competition laws. As is evident from AZTN's case law, the undertakings who behave contrary to the competition rules do indeed risk being sanctioned. In the fight against cartels, as of recently AZTN has another tool at its disposal, the so called leniency program. Under this program, the cartel participant who is the first to notify AZTN and deliver proof of existence of a cartel shall be exonerated from monetary penalty. Also, if the conditions for exoneration from penalty are not satisfied, a penalty in a diminished amount shall be levied for an undertaking who delivers to AZTN additional evidence which, along with already existing evidence, is decisive for uncovering a cartel.