If you are flying with Lufthansa via to or from any Germany airport you will not be having a good time on Monday 22 April. Also most flights in Europe on other airlines are overbooked due to this action.
Due to the announced strike actions on Monday, 22 April, nearly all Lufthansa flights within Germany and Europe will be cancelled. Only a select few short-haul flights will operate on Monday, such as in Berlin, where strike actions should end by 2:30pm CET. In all, only 20 of the 1,650 planned Lufthansa short-haul flights on Monday will operate due to the limited flight schedule.
In addition to the cancellations in Germany and Europe, massive flight cancellations and delays are to be expected for long-haul flights beginning Sunday April, 21. Of the 50 planned flights in Frankfurt, only six will operate; in Munich, of the 17 planned flights, only three will operate; whereas, in Dusseldorf all three long-haul flights are scheduled to operate as planned.
Flights operated by Germanwings will not be affected.
You can see the list of all the flights that have been affected here