French flag carrier Air France was forced to scrap around 60 percent of flights Thursday, as unions rejected a fresh offer to end a strike now in its fourth day.
Pilots' union SNPL slapped down as "largely insufficient" an offer from Air France to limit the operations of its low-cost subsidiary Transavia France, whose planned expansion has sparked the strike.
Unions fear the company will seek to cut costs by running more low-cost Transavia flights, where pilots are paid less, at the expense of Air France operations.
Pilots are also worried that the plans will entail job losses as the company sets up bases outside of France and hires pilots locally.
Air France has already offered to limit the Transavia France fleet to 30 planes -- instead of the 37 previously expected.
And management has now offered to ring-fence Transavia France from the rest of its European operations in a bid to protect pilots employed in the country.
But SNPL boss Jean-Louis Barber countered that the offer was "largely insufficient to protect French jobs."
He said the union would meet on Saturday morning to decide whether to extend the strike beyond Monday.
A week-long strike would already be the longest since 1998.
French politicians have tried in vain to bring the strike to an end, with Prime Minister Manuel Valls saying it was "incomprehensible."
Valls told French radio on Wednesday: "We have to stop this strike.
"It is regrettable that a single category of employee, in this case pilots, can bring air transport in the country to a standstill."
Air France boss Frederic Gagey has put the daily losses from the strike at 10 to 15 million euros ($13 to $19 million).