TUI flight crew in Germany are using the regulations regarding sickness to carry out a classic work to rule. If as has been reported, all the crews operating on behalf of Air Berlin report for work and then someone goes sick on every flight just before departure, then the message is pretty clear. The crew are very unhappy about what is going on and more than a little blame is down to poor communication from management.
Denti is much better informed about what you can and cannot do in Germany and I would be interested in his view. The crews are not complaining about their current conditions, but about what might happen in future. I am unclear what basis the union could ballot its members to strike in this case. It seems highly likely that there would be a vote for a a 'legal' strike, but on what basis?
The irony is that Air Berlin is locked into an expensive deal to wet lease 14 aircraft from TUI until 2019. If TUI cannot meet their obligations then Air Berlin might be able to get out of the deal, which of course would reduce jobs at TUI. If management cannot get control of the situation anything could happen.