Blockchain, by reducing transaction costs and information asymmetry, enhances trust in the digital market and paves the way for dynamic competition in technology and innovation markets. However, the increasing concentration of information and the potential to create powerful communication networks within this environment facilitate the formation of agreements and concerted practices among users. In a decentralized structure, this poses a serious challenge to competition law due to the absence of oversight and traditional regulatory mechanisms. This study, employing a comparative-analytical approach, examines the competition law frameworks of the European Union and Iran regarding collusion in blockchain environments, thereby highlighting the need to revisit traditional paradigms of Iranian competition law. The findings indicate that in private and consortium blockchains, due to limited access and more centralized control, concerted practices are more likely to occur. In contrast, in public blockchains, given the broad participation of contributors and the decentralized nature of the network, collusion will be increased by the formation of agreements and cartels. In the European Union, these actions are suspected of violating competition law and are assessed through the application of the rule of reason, taking into account factors such as network effects and the implications of data exchange. In contrast, Iran’s legal system faces a legislative gap and a lack of practical experience in this field. However, through a broad interpretation of Article 44 of the Law on the Implementation of the General Policies of Principle (44) of the Constitution and certain Articles of the Supreme Council of Cyberspace’s documents, it is possible to challenge certain instances of collusion within the blockchain environment.