Certificate of employment

Good question - but I don't know the answer. Such information is usually confidential and it does sound strange that he would include this - unless there was a reoccurring problem of someone claiming sick leave that they suspected was unfounded.

I don't know that it would cause great harm since you can explain the situation if asked but it certainly doesn't do any thing positive for your chances. I would ask him to rewrite the reference without this information but of course you have a better standing if it is actually not allowed. And people might want to avoid a lawsuit. On the other-hand, to actually bring a legal case against them for this is likely to takes years and not necessarily have much of any pay-off, while risking a lot of costs for a lawyer and court fees.

There is an organization in most cities called the Verbraucherzentrale that can often negotiate such things without a court case and is thus much cheaper by pressuring people into a voluntary compliance.