ok ask your self
How long would you work under that system. might be legal but can you keep workers.what do you do when they start bully and fighting each other to get the job done. your workers will end up hating you their co workers and bad mouthing your company to every one they know your customers will pick up on this. when they find out they can work in out of the weather and make more on min. wage with less stress you will be training new employees over and over again good luck.
I might be wrong but I have seen this before on jobs that were less physical .