I think the most important ethical aspects in this case are the working hours and hours of rest and recuperation (Proben / Ruhezeiten).
As you can see, the NV law is very intricate and often leads to discussions amongst employees. Although we are all aware of certain aspects- let´s say woking hours, not many dancers actually know this documents detailed ins and outs.
I am actually just questioning the ethics of people signing a contract they don´t really understand, or know of it´s existence. Many dancers are not German nationals and therefore not necessarily in command of lawyers German.
