The debate about a tacit collusion of price algorithms is widespread. However, not every alignment of prices that are set by algorithms is a tacit collusion. The author theoretically analyses the case law of the Court of Justice defining an agreement, a concerted practice and a collective dominance as opposed to the notion of a tacit collusion. The analysis allows to formulate the relevant aspects of these concepts that differentiate them from a tacit collusion and, therefore, determine whether the conduct in question is legal or illegal. Furthermore, these theoretical conclusions are applied to both existing and expected collusive conduct inflicted by the use of algorithms. Conditions for the various types of an algorithmic collusion becoming illegal under the Articles 101 or 102 TFEU are identified. In the light of the findings, the author elaborates on viability and effectivity of suggestions presented in theory aiming to address the suboptimal outputs caused by a tacit collusion.