A Madrid court has cited 16 air traffic controllers, including the head of their USCA union Camilo Cela, to answer questions as suspects in a criminal case concerning a wildcat strike that caused havoc at Spanish airports at the start of a major holiday in December of last year.

The 16 were called to give evidence following a suit by a group of people who were affected by the stoppage. Some 8,000 people are seeking compensation of 10,000 euros each for the damages caused to them by the strike.

The government declared a state of alert and sent in the military to take charge of control towers after the stoppage caused Spain's airspace to grind to a halt at the start of the Constitution Day holiday on December 3.

Many controllers had called in sick and failed to report for work in what the state airport operator AENA said at the time was unannounced orchestrated industrial action.

AENA and USCA had been at odds over controllers' working conditions, with the airport operator seeking to put a cap on their salaries. Some controllers were earning close to one million euros a year through extensive overtime.

AENA last month dismissed an air traffic controller in Santiago de Compostela for serious absenteeism during the strike. Another two Santiago controllers were also forcibly relocated to different airports.