Any measure that produces binding legal effects such as to affect the interests of the applicant by bringing about a significant change in his legal position constitutes a challengeable act and may be the subject of an action for annulment under Article 263 TFEU. Although a compatibility decision does not in principle adversely affect the notifying parties, the absence of such effects cannot automatically be inferred from it resulting in the inadmissibility of the action for annulment. Likewise, the decision by which the Commission changes, against the applicants’ interests, its assessment on the ancillary restrictions related to a transaction previously approved, or the adoption of an incompatibility decision where the notifying parties had declared that they would withdraw their notification before its adoption, is an act which may be challenged. On the other hand, the decision to close a procedure opened pursuant to Article 21(4) of Regulation No 139/2004, does not constitute a challengeable act where it is the result of the parties abandoning the merger.

The action may be brought by any person able to justify that one of its legitimate interests has been affected. In addition to competitors of the participating undertakings and persons whose interests are concerned by the commitments, all entities which are not parties to the proceedings but whose legal position is modified by the decision and, in particular, by the conditions and obligations attached to that decision, may bring an action. This is the case of certain indirect competitors or employees’ representative organizations – provided that the decision has an effect on their status or on the exercise of their prerogatives and duties – or candidates for their purchase. By contrast, minority shareholders of one of the notifying parties to whom the act is not addressed, do not have a direct and individual interest in bringing proceedings. The interest in bringing proceedings is assessed on the date on which the action is commenced.

In the field of merger control, the review of Commission decisions by the EU judicature is limited to formal and procedural aspects and therefore the General Court cannot substitute its own assessment for that of the Commission. However incomplete a Commission decision finding a concentration incompatible with the internal market may be, it cannot entail annulment of the decision if, and to the extent to which, all the other elements of the decision permit the Court to conclude that in any event implementation of the transaction will create or strengthen a dominant position as a result of which effective competition will be significantly impeded.