"probably the whole EU" [citation-needed]. German privacy law is very strict. This might be a good thing, don't get me wrong - but extrapolating this to all the other 27 member states is pure nonsense.
Requiring approval of the worker's council is how an employer's demand to read an employee's mail is usually handled in Germany. I did not mean to imply that it is handled the same way in the whole EU, just that unsubstantiated monitoring is likely illegal in the whole EU.
The European Court of Human Rights recently ruled that an employee's communication may not be monitored without prior notice and without specific reasons. [1]
This ruling applies not only to the whole EU, but to the 47 member states of the Council of European, including for example Russia and Turkey.
