I'm not quite sure what you mean by underpaying? If people are willing to work for a company, and everything is as promised, what's wrong with that? (If things are not as promised, the legal system can help.)
Read what I wrote again. The point of sectoral bargaining is to remove downward competition on wages as a possible competitive advantage.
> I'm not quite sure what you mean by underpaying? If people are willing to work for a company, and everything is as promised, what's wrong with that? (If things are not as promised, the legal system can help.)
What’s wrong with that is: low wages are bad. Your conceptual mistake here is thinking that jobs are “voluntary”. Most people are forced to do jobs in order to pay for food and shelter.