Anyone who says unions are no longer necessary should go and work in an Amazon warehouse for a year. Until the workforce organizes, this is going to keep happening.
My experience of unions comes as an entrepreneur in countries with sectoral bargaining. Companies representing the whole sector negotiate against unions representing most or all workers in that sector. There may be company level deals also, but they are just a side show dealing with local issues. When the deal is made, everyone is at the same level of pain and gain. If company in retail business must allow their workers to pee, so does their competitor. You don't get competitive advantage if you fuck with your workers.
It's really just matter of arranging incentives.