European competition regulators have formally outlined their concerns to Oneworld alliance partners British Airways, American Airlines and Iberia over their proposed transatlantic co-operation agreement.
The three carriers are seeking to tighten their commercial partnership through better co-ordination of operational and marketing activities, and revenue sharing, mainly on routes between Europe and North America.
European Commission regulators, who began investigating the case in April, have confirmed that they have sent a statement of objections to the airlines clarifying where they "may be in breach" of competition rules. Details remain confidential.
The carriers will be able to respond to the concerns before the Commission takes a decision on whether the tie-up is compatible with European competition requirements.
Oneworld is similarly pursuing US anti-trust immunity for the carriers' partnership, which is being arranged in parallel with British Airways' planned merger with Iberia.