Flight attendants and pursers at Lufthansa's largest hubs, Frankfurt and Munich, have been called upon to take part in the walkout, which is scheduled from 0600 to 1100 CEST (0400-0900 GMT), UFO deputy chief Daniel Flohr said in a video message https://www.youtube.com/watch?v=XrSfguFYw9c&feature=youtu.be released on YouTube.
Lufthansa called the planned strike illegal and said it would try to offer its full flight schedule.
Germany's biggest airline, which warned on profits earlier this year, is cutting costs to cope with tough price competition and high fuel prices in a sector which has seen a string of smaller airlines go bust.
UFO's Flohr said additional calls for strikes at the group's five airlines were possible at any time and the union would discuss unlimited walkouts next week.
He said UFO was demanding from Lufthansa's namesake airline a 1.8% pay increase over a half-year period.
At other airlines of the German group, the union is in conflict over issues including pay as well as part-time work and pension plans, Flohr said.
(Reporting by Thomas Seythal; additional reporting by Ilona Wissenbach in Frankfurt; editing by Tom Sims and Louise Heavens)