The aim of the commentary is to evaluate the Supreme Administrative Court’s judgment of 10 March 2021, III FSK 2552/21, with particular emphasis on the principle of trust. The main problem of this judgment is the scope of the power of attorney in tax proceedings: does it also cover appeal proceedings without an explicit statement to this effect? Doubts related to the understanding of a „tax case” as well as practical problems with the use of the PPS-1 form are also discussed. The current case law is discussed and legislative materials are presented. The conclusions include postulates of legislative amendments.