The article analyses the reasons behind the rejection of effects of the ECJ´s judgement "Landtová" (as an act ultra vires) )by the Constitutional Court of the Czech Republic in the case "Slovak Pensions XVII". It deals also with the consequences of this Union-wide unprecedented constitutional decision for the judicial review of practice of the state authorities in administrating social security.
The attention is paid also to the consequences of the said decision for the enforcement of the principle primacy of Union law in the legal orders of the member states.