To be admissible under Article 265 TFEU, an action for failure to act must be brought by a person having an interest to initiate proceedings and assumes that the EU authority has an obligation and that it has failed to fulfill it, following a request to act.  The Commission cannot therefore choose not to take account of complaints from undertakings which are not party to a concentration capable of having an EU dimension and must undertake a diligent and impartial examination of the complaints. A letter from the Commission which states that it does not have jurisdiction due to lack of EU dimension in response to an operator’s complaint of a violation of its obligation to take a decision on a concentration approved by a national authority, amounts to a defining of its position within the meaning of Article 265 TFEU.