PARIS — French air traffic controllers walked off the job at the start of a three-day strike on Tuesday, grounding hundreds of flights across the country in a protest against plans to liberalize civil airspace.

Some 1,800 flights have been canceled out of about 7,650 scheduled for Tuesday, France's DGAC civil aviation authority said, with fewer flights to airports serving Paris, Lyon, Nice, Marseille, Toulouse, and Bordeaux affected than its initial estimate of 50 percent.

Workers are concerned that European Union plans for a "Single European Sky" will adversely affect their working conditions.

Marseille airport in the south of France said on its website that it was less affected than others, with 100 flights or about a third scrapped. More than 70 flights were canceled out of Nice airport.

Britain's easyJet has said it was canceling 35 flights to Paris, 11 to Toulouse and others to Marseille, Bordeaux. and Nice.

Air France said it was canceling an unspecified number of short- and medium-haul flights.

Preparations for the maiden flight of Europe's newest passenger jet, the Airbus A350, were also affected by fallout from the strike, French transport sources said on Monday.