The article analyzes the approaches to market power of business entities-owners of transactional digital platforms. Based on the results of the analysis of scientific papers, the author comes to the conclusion that the power of the owner of a transactional digital platform over the market of goods traded using a digital platform is an aspect of the market power of such a transactional digital platform owner in the digital market, which is understood as the market of services of the owner of a digital platform for providing access to the infrastructure of a digital platform. At the same time, the influence of the owner of a transactional digital platform, who has market power in the digital market, on competition in the market of goods traded through such a digital platform is associated with the relatedness of the digital and commodity markets. For the purposes of antimonopoly regulation of the activities of owners of transactional digital platforms, a special criterion for the relatedness of commodity and digital markets should be identified — the share of transactions made in the commodity market through a transactional digital platform in the total volume of transactions made in this commodity market.