PARIS (AFP) - France braced itself for travel chaos after the country's civil aviation body urged airlines on Monday to cut flights by up to 20 per cent in Paris and some other cities due to an air controllers' strike.

The six-day strike called by a leading trade union is due to start on Tuesday.

The civil aviation agency said three-quarters of flights would be operational on average.

"Flights to southern France, Spain, Portugal, Morocco, Tunisia and Algeria leaving from Paris" would be slightly less affected, with services reduced by 20 per cent.

It asked airlines to slash flights by 20 per cent in airports in southern France to ease the pressure.

The strike, in the midst of the peak tourist season in a nation that attracts more foreign visitors than any other country in the world, follows a rail protest that affected services to foreign countries as well as domestically, and is still continuing in some areas.

The two biggest air controllers' unions, SNCTA and Unsa-ICNA, had both arranged to strike for six days from Tuesday, warning of "heavy disruption", but the SNCTA later called off its action.

The strike comes ahead of a June 30 deadline for France to present its budget plans for the sector over the next five years to Brussels.

The strikers are protesting against planned cuts between 2015 and 2019 that they say will threaten the "necessary performance and modernisation needed to ensure an efficient air navigation service in France."

The cuts form part of a European Commission plan, called Single Sky Europe, to reduce air navigation costs by organising airspace into functional blocks, according to traffic flows rather than national borders.

The strikers argue that the move will lead to a "forced low-cost" ethos in air traffic.