Air France pilots are prolonging a walkout that has grounded more than half the airline's flights all week.

Unions are angry at Air France's plans to shift much of its European operations to a low-cost carrier, Transavia. The SNPL union announced Friday they are extending the strike through Sept. 26.

The company, which is cutting costs to try to stay competitive with budget airlines, apologized to customers.

This is one of the longest strikes at Air France in several years. It reflects larger challenges for Europe's airlines and European economies trying to maintain generous worker protections while allowing companies to adapt to evolving markets.