47The principle of legal certainty seeks to ensure that situations and legal relationships arising under EU law remain foreseeable (judgment of 3 July 2019, PT v EIB, T‑573/16, EU:T:2019:481, paragraph 233) and requires that any act of the administration which produces legal effects should be clear and precise, so that those concerned may be able to ascertain unequivocally what their rights and obligations are and may take steps accordingly (see, to that effect, judgment of 27 January 2016, DF v Commission, T‑782/14 P, EU:T:2016:29, paragraph 45 and the case-law cited). That requirement applies, in particular, where the act in question may have unfavourable consequences for those concerned (see, to that effect, judgment of 11 May 2017, Deza v ECHA, T‑115/15, EU:T:2017:329, paragraph 135).