However, an annulment action brought against such letters is inadmissible in so far as it is directed against the principal amounts of the fines, the legal position of the parent companies remaining unchanged in that respect. However, in so far as such letters demand the payment of default interest, they modify the legal position of the parent companies, which were not previously required to pay default interest, their subsidiary having promptly paid the fine initially jointly and severally due. In that regard, such letters are, therefore, capable of forming the subject-matter of an annulment action.

In that regard, letters from the Commission demanding of parent companies that they pay fines imposed on them jointly and severally with their subsidiaries for breach of the competition rules, following the reduction and partial repayment of those fines vis-à-vis the subsidiary which initially paid them, produce binding legal effects in that they finally lay down the Commission’s position and are open to enforcement.

Only measures which produce binding legal effects such as to affect the interests of an applicant, by bringing about a distinct change in his legal position may be the subject of an action for annulment under Article 263 TFEU, to the exclusion of intermediate measures whose purpose is to prepare for the final decision. In order to ascertain whether a measure the annulment of which is sought is open to challenge, it is necessary to look to its substance as the form in which it is cast is, in principle, immaterial.

The power conferred on the Commission to impose fines for breaches of the competition rules covers the power to determine the date on which the fine is payable and that on which default interest begins to accrue, the power to set the rate of such interest and to determine the detailed arrangements for implementing its decision by requiring, where appropriate, the provision of a bank guarantee covering the principal amount of the fine imposed plus interest since, if the Commission had no such power, the advantage which undertakings might be able to derive from late payment of fines would weaken the effect of penalties imposed by the Commission when carrying out its task of ensuring that the rules on competition are applied.

The charging of default interest on fines is justified by the need to ensure that the Treaty is not rendered ineffective by practices applied unilaterally by undertakings which delay paying fines imposed on them. Generally, the one and only purpose of default interest is to compensate the creditor for the delay in the payment of the money owed to him because the deprivation of a money sum is always prejudicial.

In the light of that purpose, the Commission cannot rightly demand default interest in respect of a fine imposed jointly and severally on several companies, where the fine was paid promptly and in full by one the companies responsible on behalf of all, but had to be partially repaid following reduction of the fine vis-à-vis the company which paid it. In such circumstances, there is no delay in payment on the part of the companies responsible.

In that regard, it is sufficient that the company which paid the fine clearly stated that it was also paying on behalf of the others companies jointly and severally liable, without it indispensably having to fill out a common payment declaration requested by the Commission.

(see paras 109-113, 115, 116)