The move follows a breakdown in two-year talks as the company tries to implement a cost cutting programme.
A Union chief said: “All passengers are advised to assume that their flights will not take off.” .
Lufthansa said it regretted the strike threat and said retirement benefits for its flight attendants were already industry-leading in Germany.
Lufthansa is struggling to come to agreements with air crew on how to compete with low-cost carriers on short-haul flights and more efficient Gulf carriers on intercontinental routes.
Despite announcing last week it expected record profits in 2015, the German carrier says it must make cost reductions now if it is to compete in the long term.
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