Fedex has cancelled its order for Airbus aircraft and switched its order to rival Boeing instead.
Airbus blamed electrical wiring problems for the superjumbo delays
Fedex Express said it had cancelled its order for 10 Airbus A380-800F superjumbo because of delivery delays.
Instead it has ordered 15 Boeing 777 freighters - to be delivered between 2009 and 2011 - and has an option to take a further 10 aircraft.
Airbus said it regretted the decision but understood Fedex's "need to urgently address capacity issues".
Shares in Airbus owner EADS closed more than 3% lower on the French stock exchange on the news.
"The availability and delivery timing of this aircraft, coupled with its attractive payload range and economics, make this choice the best decision for Fedex," Fedex chairman and chief executive Frederick W Smith said of the decision to swap to Boeing.
A380 ORDERS SO FAR
Emirates: 43 aircraft
Air France: 10
Singapore Airlines: 10
International Lease Finance: 10
Thai Airways: 6
Virgin Atlantic: 6
Korean Air Lines: 5
Etihad Airways: 4
Qatar Airways: 2
China Southern Airlines: 5
Kingfisher Airlines: 5
Malaysia Airlines: 6
Airbus's superjumbo project has been dogged by repeated delays, which have cost senior managers their jobs and led to big customers threatening to renegotiate orders.
The problems have forced Airbus to issue three warnings of delays in the past two years.
The most recent was in October, when the firm, which has orders for 159 aircraft so far, told its customers they could face delays of up to two years.
Airbus is now expecting to deliver the first aircraft to Singapore Airlines in October 2007, almost two years behind the original schedule.
As a result of the repeated hold-ups, most of Airbus's A380 customers are deep in negotiations in the hope of improving the terms on which they are buying the aircraft.
Last month, Virgin Atlantic deferred its order for four years to 2013, while Emirates warned that it might cancel some of its order for 43 planes - Airbus's biggest order.