Air France logo is pictured at the Air France check-in at Bordeaux-Merignac airport, as Air France pilots, cabin and ground crews unions call for a strike over salaries in Merignac near Bordeaux, France April 7, 2018. REUTERS/Regis Duvignau

PARIS (Reuters) - France’s CFDT union on Sunday urged striking Air France workers to accept a management pay offer, blaming the airline’s main pilots’ union for “taking everyone hostage” and threatening the company’s future.

CFDT leader Laurent Berger made the comments amid a week-long ballot in which Air France boss Jean-Marc Janaillac is seeking staff approval for a 7 percent pay offer over four years, which has been rejected as inadequate by striking unions.

“We have the main pilots’ union, the SNPL, which is taking everyone hostage,” Berger said on Europe 1 radio, adding that ground staff would face deeper cuts if pilots’ demands were met. The SNPL is among 10 labor groupings that back the strikes.

“It’s not in the interest of ground staff to follow, because they are the ones who will end up paying,” Berger said. The centre-left CFDT is France’s second-biggest union by membership and the largest among Air France ground staff.

But the head of Force Ouvriere, another major national union, called on Air France workers to vote against the offer and condemned the ballot as an attempt to bypass unions. “The negotiations aren’t over yet,” Pascal Pavageau said on Sunday.

The industrial action has cost Air France 300 million euros ($364 million) over 11 days, and four more strike days have already been called for May.

Janaillac has vowed to quit if workers reject the pay offer in the vote, whose results are expected on May 4.

French Prime Minister Edouard Philippe warned that staff should “fasten their seat belts” for a bigger crisis if that happens.