Pretty clearly the Commissioner should have flatly refused such access. I don't know what the rules are for private parties to attempt to influence a sitting Commissioner in the midst of a procedure laid out in an international treaty that directly impacts one's pecuniary interests. Apple is not a party to a case; rather it is a beneficiary of something Ireland did, and that it the action being investigated. But Apple has had a chance to make its statements and explanations according to a process. According to the EC, the formal investigation procedure accords an opportunity for input from all those that may be affected by its investigation:
The Commission is obliged to open a formal investigation under Article 108(2) TFEU where it has serious doubts about the aid's compatibility with EU State aid rules, or where it faces procedural difficulties in obtaining the necessary information.
The decision to initiate this procedure is sent to the relevant Member State. It summarises the factual and legal bases for the investigation and includes the Commission's preliminary assessment, outlining any doubts as to the measure's compatibility with EU state aid rules. The decision is published in the EU's Official Journal, and Member States and interested third parties have one month from the date of publication to submit comments. The Member State concerned is in turn invited to comment on observations submitted by interested parties.I have not seen comments submitted by Apple according to this procedure. It seems to me that the private meeting has an appearance of impropriety. First, it was private so it does not form part of a record of information reviewed in the course of the investigation. Neither party has given any public comment regarding what was discussed. Having a private meeting deprived Ireland of its role in responding to observations submitted by interested parties, as described above. The conversation took place for the specific purpose of influencing a decision. The conversation raises the question of whether others have also private meetings, also trying to influence the commissioner beyond the procedures laid out for investigations.
I note that "All decisions and procedural conduct of the Commission are subject to review by the General Court and ultimately by the ECJ." The Commissioner will not likely seek review of its own decision. I do not know whether other member states could seek such a review. It seems most likely that Ireland could seek a review, which it would only do if the decision was unfavorable. If that were to happen, would Tim Cook also have private meetings with the judges of the ECJ?
I should hope not.