The giant services sector union Verdi has called for the walkout at Germany's major airports over a pay dispute.
"The airlines of the Lufthansa group expect substantial disruptions to air traffic tomorrow, due to the strikes called
by Verdi," it said in a statement today.
It quoted media estimates that around 6,000 employees in Frankfurt alone would take part in the strike.
"But there will also be disruptions in Munich, Duesseldorf, Cologne-Bonn, Stuttgart, Hamburg and Hanover," the statement added.
"In view of the strikes, Lufthansa is cancelling almost all domestic and European connections in Frankfurt and Munich
until 2:00 pm (1300 GMT)."
Also affected would be long-haul connections to and from both Frankfurt and Munich, Lufthansa warned.
Flights operated by the Germanwings subsidiary and the regional carriers to and from Munich would not be affected.