According to the Enlarged Board of Appeal in G 5/91 (OJ 1992, 617) the practice that a partiality objection made at first instance is decided by the director of the department concerned cannot be considered illegal in view of the administrative character of the first-instance departments, which are subject to internal instructions by the President under Art. 10(2)(a) EPC (see also T 2509/11 and T 71/99). Under the EPC there is no legal basis for any separate appeal against an order of a director rejecting a partiality objection to a member of a department of first instance such as an opposition division. However, the composition of the opposition division can be challenged on appeal against the final or interlocutory decision of the division. If not all the members of an opposition division fulfil the requirement of impartiality, there is a procedural violation which would normally render the decision void. The Enlarged Board of Appeal made it clear that it lay within the competence of the boards of appeal to decide whether this requirement had been fulfilled. This was also done in practice (cf. e.g. T 251/88, T 939/91, T 382/92, T 476/95, T 838/02, T 1349/10). Such consideration might take place of the boards' own motion or at the request of a party to the appeal proceedings.

In T 479/04 the board found that G 5/91 did not prohibit an opposition division from deciding itself on an allegation of partiality made against it. Moreover, it could not be inferred from G 5/91 that it was forbidden to decide on that matter together with the decision on the substance. The board concluded that the opposition division had not committed any procedural error by deciding itself, as part of the contested decision (see also T 1647/15).