Sir Richard Branson's airline Virgin Atlantic today urged the European Commission to reject the planned tie-up of British Airways and giant US carrier American Airlines (AA).
In a document to the EC, Virgin said the link-up would lead to BA and AA raising fares and adjusting schedules to keep out competitors.
Virgin added that BA/AA would have a monopoly or be dominant on some of the busiest and most profitable routes between the US and Heathrow.
BA and AA would control 64 per cent of the capacity between JFK New York and Heathrow, Virgin said, and 64 per cent between Chicago and Heathrow, 80 per cent between Boston and Heathrow, 73 per cent between Miami and Heathrow, and 100 per cent between Dallas Fort Worth and Heathrow and Seattle and Heathrow.
Virgin chief executive Steve Ridgway said: "We urge the EC to reject outright this third attempt by BA and AA to stifle competition between Heathrow and the US.
"Their virtual merger would lock-up one of the world's busiest air corridors against new and existing competition, increase BA's grip on the most constrained international airport in the world and cause grave harm to consumers with higher prices."
He added: "Even if BA and AA were forced to give up (take-off and landing) slots at Heathrow, these so-called slot remedies on their own would not be suitable as they would be insufficient to reinstate any effective level of competition.
"They would not cancel out anti-competitive effects arising out of the increased network reach planned by BA and AA."