This article aims to show the similarity between the arguments developed regarding the Treaty freedoms and the approach to the legal principles proposed by R. Alexy. Treaty freedoms from the Treaty on the functioning of the European Union, developed in the course of the Court’s many years of judicial activity, have a number of similarities to the concept of the principles of law proposed by prof. Robert Alex. This is evidenced by – the position of the principles of law in the legal system, the possibility of grading them, or a separate method of resolving the conflict of two opposing principles of law. The article analyses selected treaty freedoms in relation to tax matters and compares them with theoretical schemas proposed by prof. Robert Alexy.