Virgin Atlantic has officially registered its protest with the European Commission against International Airlines Group's proposed takeover of UK airline BMI, claiming that passengers will be the biggest losers if the deal goes ahead.
Virgin said that if the takeover is approved British Airways would have a "monopoly" on three domestic routes to Heathrow - from Edinburgh, Aberdeen and Manchester - and competition to certain European destinations would be "eradicated".
As a result, BA would look to increase fares and cut services on those routes, said Virgin, "backing passengers into a corner with no alternative carrier".
It bases its claims on traffic data from the Heathrow-Glasgow route following BMI's withdrawal of services in early 2011, leaving BA as the sole operator. "This resulted in average fares paid by passengers increasing by 34%. It also shows how the number of flights on the route decreased by nearly half - not only from the loss of the BMI flights, but because BA also reduced its own flights on the route by almost 10%," said Virgin.
Richard Branson, president of Virgin Atlantic, said: "This takeover would take British flying back to the dark ages. For years pioneering airlines have fought to provide consumers with more choice and lower fares. This move will see British Airways unravel all of this progress made.
"This merger will see BA holding more than half of all take-off and landing slots at the UK's only major international hub - an airport that has had much needed growth plans forcibly frozen. The regulators cannot allow British Airways to sew up UK flying and squeeze the life out of the travelling public."
It also claimed if the deal was given the green light, BA's dominance of slots at Heathrow would harm competition.
In response, IAG said it remained confident that the European competition authorities would approve the acquisition.
"BMI is a massively loss-making airline. Selling it to IAG offers the best solution for British consumers and UK plc, securing more jobs than if the airline was broken up and sold-off for its Heathrow slots," said IAG in a statement.
"Far from cutting back, British Airways added 4000 weekly seats on its services from Heathrow to Glasgow last year. Virgin Atlantic has never flown to Scotland and, as far as we know, has no plans to do so."
Including BMI's share, IAG would have 53% of Heathrow slots, it said, which compares favourably with Lufthansa's 66% share at Frankfurt and Air France-KLM's 59% and 57% share at Paris Charles de Gaulle and Amsterdam Schipol, respectively.
IAG submitted its notification of the acquisition to the commission on 10 February, which has 35 working days to make an initial decision.