Lufthansa's ground staff will go on a strike on Wednesday upon the call of the Verdi union to boost its leverage in salary negotiations.
The strike is scheduled to start at 3:45 a.m. (1:45 a.m. GMT) on Wednesday and last until 6 a.m. on Thursday.
Lufthansa was initially unable to say how many flights would be canceled as a result, but described the planned walkout as "unreasonable."
"This is all the more incomprehensible as the employer side has already offered high and socially balanced pay increases," said human resources chief Michael Niggemann, according to a statement.
He added that the negotiations were taking place against the backdrop of a "tense economic situation for Lufthansa after the coronavirus pandemic, high debt burdens and uncertain prospects for the global economy."
Steffen Kampeter, the head of the Confederation of German Employers' Associations BDA, said: "To burden Lufthansa and above all its passengers with wage demands in the middle of the summer is absolutely disproportionate."
"People's understandable desire for holidays is being shamelessly exploited to gain an advantage," Kampeter added.
Verdi is negotiating on behalf of about 20,000 ground staff crew members, including technicians and logistics workers, without whose services the planes cannot take off.
Verdi had rejected an initial wage offer from Lufthansa but agreed to continue negotiations on Aug. 3-4. The union is demanding a 9.5% pay increase.
In view of the workload, high inflation and wage sacrifices during the pandemic, significant wage increases are justified, said negotiator Christine Behle.
Lufthansa has been forced to scrap thousands of flights to and from its national hubs Frankfurt and Munich this summer due to severe staff shortages and increased demand.
Verdi blames mismanagement at airports and airlines for the chaos.
