Ryanair claims it and other airlines at Stansted are being discriminated against.
The carrier has looked at air traffic control delays in the London area over three months.
It says 52% were at the Essex airport - with just 10% at Gatwick and none at Heathrow.
"Ryanair and Stansted are clearly being discriminated against by the UK airline owned ATC provider Nats," said Ryanair’s Peter Bellew. "Nats don’t have enough staff"
"The situation is particularly bad at weekends where Nats are hiding behind adverse weather and euphemisms such as 'capacity restrictions' when the truth is they are not rostering enough ATC staff to cater for the number of flights that are scheduled to operate.
"Urgent action must now be taken by the UK Dept of Transport, and the EU Commission, otherwise thousands more flights and millions of passengers at Stansted will continue to suffer disproportionate delays, while Nats protects its shareholder airlines’ services in Heathrow and Gatwick."
Provider Nats says it cannot be blamed for Ryanair's performance over the summer.