The current economic understanding of the effect of labour unions on employment and wages What are the currently largely accepted views on the effect of labour unions on employment and wages? Where can I read more about the currently established theoretical models that model labour unions?
I'd recommend checking out Labour Economics by Borjas.
It is such a broad topic that really quite a detailed evaluation would have to be conducted.
In particular, the effect of a labour union on levels are unemployment are likely to be affected by the assumptions in your theoretical model.

Assumptions of perfect and imperfect competition (of some type) are likely to have different signs and magnitudes.

It follows that it is perhaps useful to look for empirical evaluations on the matter. Personally, it's not my field - but it is possible that someone like Borjas has done research, or potentially Kreuger.