Airbus suffered a double blow on Tuesday as airlines warned they faced further delays on delivery of the A380 superjumbo and a new hitch developed with the plane maker's cost-saving plans.

Dubai's Emirates airline, the biggest A380 customer, and Abu Dhabi-based Etihad Airways, both said they had received warnings of delivery delays on the world's largest passenger airliner -- which is already two years behind schedule.

Airbus confirmed that chief executive Tom Enders had written to all A380 customers telling them production had reached a critical phase. It announced a 'major review' of A380 production last week.

Separately, in Toulouse, French labour unions claimed victory in their battle to stop Airbus from selling some factories -- a plan that is part of a major restructuring and job-cutting exercise.

The A380, which went into service last year with Singapore Airlines, is heavily bankrolled by state-owned Emirates, which has ordered 58 A380s.

'This will do us serious damage,' Emirates president Tim Clark told Reuters by telephone in Dubai.

Deliveries of the A380 have fallen behind schedule after a series of industrial mishaps since 2005. The reputation of Airbus parent firm EADS is seen at stake as it strives to deliver 13 planes this year.

Emirates, the largest Arab carrier, hopes to receive five A380s before the end of March 2009 and another 12 in the year to March 31, 2010. Clark said he will find out in the next two to three weeks whether that schedule is intact.

A spokesman for the Abu Dhabi government-owned carrier, Etihad, said it too had received a letter from Airbus indicating that there may be a delay.

Etihad has ordered four of the $300 million, 525-seat planes.

Europe's biggest single industrial project first faced upheaval in 2006, when A380 sections reached the French assembly plant with wiring flaws that caused production to halt.

The news sliced a quarter off EADS stock and triggered management upheaval.

Airbus blamed the failure of German and French plants to use the same design software, and was forced to start assembling the first 25 planes by threading the 500 km of wiring through each aircraft manually, pushing deliveries back on average 2 years.

In a separate development on Tuesday, unions and industry sources in France said plans to sell two factories to attract investment in new lightweight airframe materials were showing signs of unravelling. The news follows the collapse of talks to sell some factories in Germany.

The potential double setbacks highlights the internal and external pressures squeezing Airbus parent EADS as Europe's largest aerospace firm scrambles to hold together its production system while resisting the global financial crisis.

A380 production problems are a legacy of internal rivalries, which until recently prevented French and German factories developing a common system for wiring the double-decker jet, hurting political pride in Europe's biggest industrial project. - Reuters