The pilots' union Vereinigung Cockpit said in a statement it is "planning... Strikes for all Germanwings flights departing from all German airports between 6:00 am and midday" (local time) tomorrow.
Cockpit had already said last week that it was ready to stage walkouts over its demands for better provisions for pilots nearing retirement age.
"At the same time, Cockpit has said it is prepared to reach an agreement at any time to avert the strikes," it said.
Cockpit already grounded thousands of flights of the parent company Lufthansa during three days of strikes in March and April in pursuit of its demands, costing the airline around 60 million euros (USD 79 million).
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Lufthansa said it "very much regrets this strike announcement and particularly the inconvenience it will cause Germanwings customers".
The airline said it was "looking into what impact the strikes will have on the talks with the union".
A spokeswoman for Germanwings said that around 164 flights would be affected by the six-hour walkout.
It said it was drawing up an amended timetable for the period in question.
Any Germanwings flights operated by Eurowings would not be affected, it added.