Currently there is none in certain instances. If a single mother with two kids under school age is on TANF and food stamps and stays at home to care for her kids she has no incentive to go out and start at the bottom of the ladder because she'll be worse off after paying for daycare.
If, however, there was a procedure in place that would allow her to work while receiving those benefits, with that benefit reducing as she moved up the pay scale- then they'll have an incentive to work: more $$.
Now that assumes, of course, employers are offering a system that will allow for advancement up a pay scale... and a lot of menial labor jobs don't have that system.
It's a complex situation, and how we work our way out of it is even more complex.