Ryanair has said it will cut capacity at Stansted to cut costs
BAA is taking legal action against Irish airline Ryanair for non-payment of landing fees.
The UK's largest airports operator is suing Ryanair for failing to pay charges for use of Stansted airport. Ryanair has vowed to fight the action.
The row broke out in April when BAA raised its charges and Ryanair said it would not pay the "excessive" fees.
The news came as the airline revealed it carried 5.66 million passengers in July, up 19% on the last year.
However, Ryanair's planes were only 89% full last month compared with 90% at the same time in 2007.
Meanwhile, the group also warned last month that it was on course to post an annual loss of up to 60 million euros (£47.4m) due to high oil prices.
At the time, the Irish airline announced it would be cutting the number of aircraft using Stansted airport in Essex during the winter by a third, to offset both high fuel costs and increased fees levied by BAA.
"Unlike Ryanair, we have no wish to conduct our business in public, via the media. This matter is in the hands of the lawyers so it is inappropriate to make any comment at this stage," a spokesperson for the group said.
The group added that the rise in tariffs was within the limits allowed by industry watchdog, the Civil Aviation Authority.
It also said Ryanair had "enjoyed substantial discounts" for using Stansted in the past but these ended on 1 April 2007.