East Midlands International Airport (EMIA), owned by Manchester Airports Group (MAG), and Prestige Parking Limited broke competition law, but the airport was spared the fine after disclosing full details of the wrongdoing.
An investigation by the CAA found the two had agreed Prestige should not sell its car parking services at the airport below a minimum price, linked to the price of the airport's own car parking services. It said East Midlands "imposed this requirement" as a condition of allowing Prestige to access facilities at the airport between (at the latest) October 2007 and September 2012.
Competition law doesn't allow independent businesses to make such arrangements as they can restrict competition.
The CAA said EMIA and owner MAG, which also owns London Stansted airport, would have had to pay nearly £12.5m as a result of the decision, but "the company proactively disclosed details of the agreement under the Competition and Market Authority's (CMA) leniency programme before the CAA investigation began".
So the fine was reduced to zero in line with the CMA's policy.
Richard Moriarty, director of markets and consumers at the CAA, said: "The fact that an airport operator owns land at the airport on which an independent business operates, does not mean that the airport can dictate the price of services sold by that independent business."
As the CAA's first competition investigation, he said it should serve as "a clear sign" that it's "prepared to take action to protect consumers wherever necessary", and there is the prospects of a hefty fine should companies break competition law.
The decision was taken in the midst of a wider review of road-based access to UK airports, including competition issues in areas such as car park provision.