Some 37,500 passengers would be hit by the nine-hour strike scheduled to begin at 1300 GMT and affecting the Frankfurt and Duesseldorf airports, Lufthansa said in a statement.
"Around 10 percent of all flights will have to be cancelled. Of a total 3,000 connections scheduled for today, 290 flights will be cancelled, including 23 inter-continental services," the statement said.
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Lufthansa cabin staff will begin their planned week of walkouts at 2 pm on Friday, initially at the hubs of Frankfurt and Düsseldorf, with further stoppages planned on Saturday, the union UFO said.
The strike on Friday will be for nine hours and last until 11 pm, UFO said in a statement.
The union plans to stagger the walkouts and target different airports over the course of the next seven days, with a repeat of the stoppages planned in Frankfurt and Düsseldorf on Saturday.
However, Lufthansa's Munich hub would not be affected at all this weekend, given that there were still school holidays in the southern regional states of Bavaria and Baden-Württemberg, it explained.
In addition, "no industrial action is planned at all on Sunday since most people travelling that day will be doing so in a private capacity," UFO said.
UFO had announced on Thursday that industrial action was "unavoidable" after management had failed to come up with an improved offer in a long-running dispute over pay and early retirement provisions.
Lufthansa said it "regretted" the short notice of the strikes, which would put passengers "in a very difficult position."
It insisted that it had conceded to all of the union's demands.
Only Lufthansa passenger services would be hit, while the subsidiaries Air Dolomiti, Austrian Airlines, Brussels Airlines, Eurowings, Germanwings, Lufthansa CityLine and Swiss would not be affected, the airline said.
The UFO union said it will give sufficient advance warning of when the strikes will take place.
It is first time that cabin staff have staged walkouts in the nearly two-year long dispute.
UFO is demanding the current system of early retirement provisions remain unchanged.
The dispute with cabin staff is separate from a long-running battle between management and pilots over company plans to change the pilots' early retirement arrangements.
Lufthansa wants to scrap an arrangement under which pilots can retire at 55 and receive up to 60 percent of their pay until they reach the statutory retirement age of 65.
Pilots, who are concerned about Lufthansa's aim to further develop its low-cost activities as it faces growing competition, have staged repeated walkouts during the dispute.
Last week, Lufthansa said it was raising its full-year forecasts after low oil prices and positive passenger numbers lifted profits in the third quarter.