How to force taxonomy on role or content type?

I am making a site for two groups of users ('group a' and 'group b'). Based on the taxonomy of the node, it displays for either of those groups (so you tick a selectbox to make a page available to 'group a', 'group b' or both). Now there are two types of content managers that can make pages. One can make pages for 'group a' and 'group b' and one can only make pages visible to 'group b'.

How can i force it so that content manager 2 can indeed only make pages for 'group b'? I was thinking of a custom content type that always had taxonomy 'group b' or limit it by role, but i can't find how it's done.

Any help would be appreciated.