Customer service at Stansted airport must improve and security queues must be cut - or its owner will be fined.
That is the message from the Civil Aviation Authority, which is bringing in a penalty system at the Essex airport similar to the one in place at Gatwick and Heathrow.
All three are owned by the BAA, which will have to pay rebates to airlines if it gives customers at Stansted poor service.
Areas such as security queues, the cleanliness of the terminal, flight information and baggage reclaim will be looked at.
The CAA said in a statement that service at the airport had been "unacceptably low" during the past five years.
Ryanair, one of the airport's major airlines, went further, describing service quality as "abysmal".
Head of legal and regulatory affairs Jim Callaghan said: "BAA provides very poor service levels to customers, as witnessed by Monday's unacceptable serious security breach and horrendous security queues."
On Monday climate change protesters chained themselves to fencing in a secure area near the runway, forcing the cancellation of dozens of flights.
The CAA also refused to raise landing charges at Stansted to the level BAA had asked for over the next five years.
The charge per passenger levied on airlines using the airport will rise from £6.34 this year to £7.05 in 2013-14.
BAA said it needed to pay for new infrastructure at the airport, including a new terminal and a new runway, but easyJet and Ryanair believe it should not be allowed to raise the landing fee at all.
Mr Callaghan said: "The prices announced by the CAA are still out of line with what efficient airports are offering throughout Europe."
Easyjet added in a statement: "Keeping prices broadly flat over the coming years should ensure consumers continue to be protected from BAA's worst excesses."
The proposals are under consultation until February.
The Competition Commission will also report on whether BAA's control of London's airports is anti-competitive next year.
It is expected to call for the sale of Stansted and Gatwick, which is already on the market.
Prices for Stansted Mid Stay airport parking start at just £7.36 per day.
This price is correct for bookings searched on December 9, 2008. Prices are subject to change. Book your Stansted airport parking in advance to get the best prices and availability.