PARIS, France (AFP) – French air traffic controllers are to stage a one-day strike Thursday which risks seeing most flights cancelled at both main Paris airports, France’s leading aviation association said.

Unions called the strike after the breakdown of negotiations on salary hikes 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 which Paris is due to host from late July when hundreds of thousands of extra visitors are expected.

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. Regional airports are also set to be badly affected.

“It will have a huge impact,” he 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 need to be accompanied by higher salaries.