French air traffic controller strike threatens flight chaos

French air traffic controllers are to stage a one-day strike on Thursday that risks seeing most flights cancelled at the two main Paris airports, France's leading aviation association warned on Tuesday.

Unions called the strike after a breakdown of negotiations on salary increases and other measures in a planned overhaul of France's air traffic control system.

The action has raised new concerns over the risk of strikes during the Olympic Games that Paris is due to host from late July, when hundreds of thousands of extra visitors are expected.

The main air traffic union has also warned it could order several days of strike action over a busy May holiday weekend if its demands are not met.

The strike is going to be "very strongly followed", said Pascal de Izaguirre, the head of FNAM, an umbrella group of French aviation industry unions.

He said 75 percent of flights could be cancelled at Paris Orly airport and 65 percent at Charles de Gaulle, the capital's main airport.

Those figures were confirmed late on Tuesday by a source with knowledge of the cancellations, with airlines also being forced to cancel 65 percent of flights in the southern city of Marseille.

France's DGAC aviation authority is also telling airlines to cut 60 percent of flights at both the Toulouse and Nice airports, and 50 percent at other regional airports.

"It will have a huge impact," de Izaguirre said.

On top of the cancellations, "major delays" are to be expected, said an official from the air traffic controllers' union, asking not to be named.

The air traffic control reforms aim to improve productivity but unions think the changes should be accompanied by higher salaries.

The main air traffic union, the SNCTA, has also issued notice it could strike on three days, from Thursday May 9 to Saturday May 11.

This could potentially wreck many people's holiday plans, with May 9 a public holiday and May 10 traditionally used as a "pont" (bridge) to make a long weekend.

In a statement, the union condemned the failure of the discussions "in particular on the question of social support" and gave authorities two weeks to "engage in a search for solutions" before it carries out the strike threat.