26) In support of their appeal, the appellants raise four grounds, alleging, first, infringement of Article 10(3) TEU, of Article 15(1) and Article 298(1) TFEU and of Article 42 of the Charter of Fundamental Rights of the European Union (‘the Charter’), in conjunction with Article 52(1) of the Charter, second, failure to fulfil the obligation to state reasons, third, infringement of Article 4(2) and (3) of Decision 2004/258 and, fourth, infringement of Article 4(3) of that decision.

...27) By their first ground of appeal, the appellants claim that the General Court failed to apply the principle of transparency laid down in Article 10(3) TEU, Article 15(1) and Article 298(1) TFEU and Article 42 of the Charter, in conjunction with Article 52(1) of the Charter, in the light of which the exceptions provided for by Decision 2004/258 should have been interpreted.

...

29) By the first part, the appellants criticise the General Court for having held, in paragraph 29 of the judgment under appeal, that the exception provided for in the first subparagraph of Article 4(3) of Decision 2004/258 does not require it to be established that the decision-making process could be seriously undermined. In that regard, the appellants claim that the General Court wrongly relied on the wording of that provision, and criticise it for having adopted an interpretation of that wording which is not consistent with Article 10(3) TEU, Article 15(1) and Article 298(1) TFEU and Article 42 of the Charter, in conjunction with Article 52(1) of the Charter. They assert that those provisions lay down the objective of broad transparency and a right to access to documents which the General Court failed to apply.

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32) By the second part of the first ground of appeal, the appellants criticise the General Court for having, in paragraph 54 of the judgment under appeal, conferred on the ECB a broad discretion and thus reduced the scope of its judicial review, in breach of primary law, with the result that the assessment carried out in paragraph 43 et seq. of that judgment was flawed. They take the view that, on account of the dimension of the principle of transparency, access to documents is not a matter for assessment. Article 52 of the Charter requires that any restrictions on that principle be proportionate and that the conditions for applying such restrictions be amenable to full judicial review.

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37) In those circumstances, and since the appellants did not expressly claim before the General Court that, for that reason, the first subparagraph of Article 4(3) of Decision 2004/258 undermined the principle of transparency, as laid down by the provisions of the FEU Treaty and the Charter that they rely on, it must be held that such a plea of illegality was not raised at first instance and cannot, subsequently, be relied upon for the first time in the appeal.