In accordance with established case law, an opposition division has the discretionary power to introduce of its own motion a fresh ground for opposition (Art. 114(1) EPC). With regard to the opposition proceedings the Enlarged Board of Appeal stated in G 10/91 (OJ 1993, 420) that exceptionally, the opposition division may in application of Art. 114(1) EPC consider other grounds for opposition which, prima facie, in whole or in part would seem to prejudice the maintenance of the European patent. With regard to the appeal proceedings the Enlarged Board of Appeal held that fresh grounds for opposition may be considered in appeal proceedings only with the approval of the patentee. On the extent to which an opposition division should examine new grounds for opposition, see chapter IV.C.3.4.4.

The board's review of the discretionary decision of the opposition division is essentially limited to ensuring that the opposition division did not use this power unreasonably (T 1340/15).

In T 1119/05 the objection under Art. 100(b) EPC was already raised, although belatedly, before the opposition division which decided not to admit this late-filed ground. The board introduced the documents referred to in support of the objection in order to assess whether the opposition division had exercised its discretion properly. Having found no indication that the opposition division had exercised its discretion in an unreasonable way, the board saw no reason to reverse the decision of the first instance (see also T 839/14).

The board in T 109/08 held that, when reviewing an opposition division's exercise of discretion in deciding under Art. 114(2) EPC not to admit a late-filed ground for opposition, the boards had the power to overrule its decision if they concluded that it was based on manifestly incorrect technical assumptions or on an erroneous approach to applying the ground in question, since that would amount to a misuse of the discretionary power under Art. 114(2) EPC. The case was remitted to the department of first instance for a new decision.

In T 1286/14 the board addressed the limited scope for reviewing exercises of discretion to refuse a "fresh ground for opposition" where the proprietor objects to its admission on appeal. In the case at issue, the opposition division had considered a late-filed ground irrelevant and refused to admit it. In such circumstances, it was sufficient for the board to establish that there was evidence that the opposition division had actually examined whether the ground was prima facie relevant and given reasons for its finding on this. So, instead of reviewing whether the opposition division had examined such prima facie relevance "correctly" in substance, it merely had to check that such an examination had demonstrably been conducted. In other words, its duty to review the exercise of discretion was limited. Citing G 10/91 (OJ 1993, 420), it thus refrained from examining the substance of the fresh ground, thereby following the approach taken in T 736/95, OJ 2001, 191; T 1519/08 and T 1592/09 and rejecting that entailing a thorough review of the earlier exercise of discretion on its merits, as taken in e.g. T 1053/05, T 1142/09 and T 620/08.