54According to settled case-law, in an action for annulment, a plea which is a matter of public policy may be invoked by the parties at any stage of the proceedings, since such a plea may, or even must, be raised by the EU courts of their own motion (judgments of 8 July 2004, Mannesmannröhren-Werke v Commission, T‑44/00, EU:T:2004:218, paragraph 210, and of 14 April 2015, Ayadi v Commission, T‑527/09 RENV, not published, EU:T:2015:205, paragraph 44; see also, to that effect, judgments of 20 February 1997, Commission v Daffix, C‑166/95 P, EU:C:1997:73, paragraphs 23 to 25, and of 3 May 2018, Malta v Commission, T‑653/16, EU:T:2018:241, paragraphs 47 and 48). According to the same case-law, a plea alleging failure to state or failure sufficiently to state the reasons on which an EU act is based is a matter of public policy.