In this paper the author examines the legal regime of the plea of illegality regulated by Article 4 of the Law on administrative disputes No 554/2004, as this text has been rather recently amended by Law No 76/2012 for the implementation of Law No 134/2010 on the [new] Civil Procedure Code. In this regard there are examined: the definition and the legal nature of the plea of illegality, its features, as well as the conditions of admissibility of the plea of illegality.