Under Art. 105(2) EPC in conjunction with Art. 2(1) No. 10 RFees, interveners must pay the opposition fee (see R. 89(2), second sentence, EPC; T 27/92 of 25 July 1994 date: 1994-07-25).

Where a party intervenes only at the appeal stage, several decisions have stated that no appeal fee need be paid if the party is not seeking appellant status in his own right (see T 27/92 date: 1994-07-25, T 684/92, T 467/93, T 471/93, T 590/94, T 144/95, T 886/96 and T 989/96). In T 1011/92 and T 517/97 (OJ 2000, 515) the board ruled that an intervener must pay the fee if he wants to have his own right to appeal proceedings, in the sense that he can continue them if the original appellant withdraws his appeal. However, in T 144/95, where an intervention was filed during appeal proceedings and an appeal fee paid, the board ordered the appeal fee to be refunded (at the request of the intervener) – under Art. 107 EPC 1973, an admissible appeal could only be filed by a party who was already a party to the proceedings leading to the decision and who was adversely affected by it. Where the intervention was filed during appeal proceedings, the intervener could not satisfy these conditions, and, referring to G 1/94, OJ 1994, 787, could not be considered as an appellant. Whilst Art. 105 EPC 1973 provided an exception to the time limit for payment of the opposition fee under Art. 99 EPC 1973, no such exception was made concerning the appeal fee.

In G 3/04 (OJ 2006, 118) the Enlarged Board held that there was no legal basis for demanding the payment of the appeal fee by an intervener in appeal proceedings. Fees paid by way of precaution but without a legal basis were reimbursed.