Airlines have slashed flights in France as a strike by air traffic controllers fearful of a plan to unify European skies went into full force.

The Civil Aviation Authority has asked airlines to cancel one out of two flights at Orly airport, south of the French capital, and one out of five flights at Charles de Gaulle, the main Paris airport.

The strike which began on Tuesday night night went into full force on Wednesday and was to last until around 6 a.m. (0400 GMT; Midnight EDT) on Thursday.

National carrier Air France has said its long—haul flights aren’t affected.

Air traffic controllers fear that the Single European Sky concept meant to deal with projected traffic increases could cost jobs.

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