Germany's Lufthansa said it will have to cancel 800 flights on Friday, likely affecting 130,000 passengers, after the pilots' union announced a one-day strike.

The Vereinigung Cockpit (VC) union said late Wednesday that pay talks failed and Lufthansa pilots would stage a 24-hour strike starting just after midnight on Thursday, affecting both passenger and cargo services.

Lufthansa said flight cancellations would affect Frankfurt and Munich airports, adding that several flights would also have to be canceled on Thursday.

VC is demanding a 5.5% pay rise this year for its more than 5,000 pilots and automatic inflation compensation thereafter.

"We hope to get back to negotiations as soon as possible," a Lufthansa spokesperson said on Thursday. "However, we cannot bear the cost increases associated with VC's demands either," he added.

Strikes and staff shortages have already forced airlines, including Lufthansa, to cancel thousands of flights this summer and caused hourslong queues at major airports, frustrating holidaymakers keen to travel after COVID-19 lockdowns.

Lufthansa has already faced strike action this year by security workers and ground staff over pay.

The airline said it was doing everything possible to minimize the effects of Friday's pilots' strike, but it could not rule out cancellations or delays in some cases over the weekend.

Shares in the airline were down 3.5% at 9:30 a.m. GMT.

Michael Niggemann, the Lufthansa executive board member responsible for human resources, said the strike was incomprehensible and defended the airline's "very good and socially balanced" offer.

Lufthansa has offered a total of 900 euros ($901.35) more in basic pay per month in two stages over an 18-month term as well as an agreement guaranteeing cockpit staff a minimum fleet size.

Germany's cartel office on Thursday also prohibited Lufthansa from ending long-term cooperation agreements with charter airline Condor until further notice, saying the national carrier was impeding Condor from competing on long-haul routes.

Lufthansa said it took note of the cartel office's decision, adding: "However, we do not share the Bundeskartellamt's view and will therefore submit the decision to a judicial review."