Conflict of interest, capture of union representatives by employers etc.
Basically "Everybody's happy, what's not to like?" is the go-to justification for corruption.
Remind me: Where is it allowed again that "the union does some of the employer's HR department's work as well"? Asking for a friend ...
@glitzersachen @doctormo The UK.
For example, an employee, not necessarily knowing who's best placed to answer a query, might go to their union rep rather than their line manager or HR to ask "How do I ...? How does ... work? What would happen if ...?" and if the union happens to know the right answer then that saves HR and/or management time. (Of course the union will signpost them on when appropriate, eg if they don't know the answer or it's not their business to give it.)