In my country the minimum wage is set / month, not / hour so it's easier for me to discuss it this way.
Let's say I usually pay the worker $350 / month to work in my garden 6 hours / day in an office. Then, a "MW" Law comes along that sais I have to pay him at least $600.
I can't fire him just because he's being overpaid - I need his services! So I go to the worker and say "Listen, man, from now on you're going to have to do more stuff around here, such as mow the lawn and clean the room since I pay you extra".
I might not need that extra work, but I absolutely require what I hired him for, so I'm going to keep him around and use him for other stuff too, like a henchman.
That is, until a gardening company comes along that does my garden for $200 / month :)