Thousands of Airbus SE workers in the U.K. are set to walk off the job for 10 days in September after 90% of union members voted to strike over the aircraft manufacturer’s pay offer.

The industrial action will start on September 2 and continue over a three-week period at Airbus wing factories in Broughton and Filton, according to Unite, a union that represents more than 3,000 Airbus engineers and aircraft fitters.

Both sites could temporarily close down because of how many union members are based there. Wings for the A320, A330 and A350 jets are produced at the factories, representing a critical part of Airbus’ supply chain. Airbus is under pressure to ramp up deliveries after a flurry of big orders for narrowbody and widebody jets.

Airbus is not concerned about the strike affecting its year-end delivery schedule, Sue Partridge, Airbus U.K. country manager of commercial aircraft, said in a statement. She called the company’s wage offer this year “competitive and fair” and said pay increases have totaled more than 20% in the last three years.

Unite said the strike would disrupt production across commercial and military aircraft programs and delay deliveries. The union has asked Airbus to return to the negotiating table with a pay offer that accounts for inflation and workers’ high-quality skills. 

“Airbus is generating billions in profit; workers deserve a fair deal,” Unite General Secretary Sharon Graham said in the statement. “Our members are simply seeking fairness not favours.”