Is there a union for that workplace?  I'm not too familiar with German unions.  It does go to show how effective it can be when all the little people make a stand together.  But you need everyone to be involved to have the impact.  

Rights for temps are an issue in the UK also and employers are making more and more use of temps in order to save money and to legally sack those who are potential troublemakers.

A union presence would be ideal here (although I am assuming that the same rights exist in Germany that protect union members and reps from unfavourable treatment or victimisation).  In the UK, where workplaces are unionised it can be very effective when unions and management work together to improve conditions.  It isn't always about strikes and conflict.

It's ridiculous how short sighted management can be when they try to cut costs or introduce changes.  At the end of the day they are dealing with real people, real impacts on lives.  Stupid shifts, lack of attention to health and safety, and a disregard for staff will cause problems and costs for the employer in the long run.