House/building painting isn’t a very difficult job. I don’t say this disparagingly; working in construction, I’m certainly aware of aspects of the professional painter’s job that require skill and patience that I myself often lack (or have little interest in developing). That painting tasks exist for which one is well advised to hire an experienced professional, however, does not mean that a particular job requires workers who obsess over the bristles in their brushes.
So there’s a simple answer and an extending tangent to BAM’s comment to my most recent post:

Are you implying that the market rate for painters (non-union? union?) is $7.40 per hour? I would suggest to you that this young woman and young man are, in fact, being cheated by the Little Compton School Committee.

In one sense, this is a prima facie matter: The fact that two adults, acting of their own free will and presumably not based on a life-or-death incentive, have accepted the terms shows that $7.40 is indeed the market rate for this particular job. Professional painters who can expertly patch drywall, glaze windows, and clear-finish fine carpentry work can surely command more, but as it happens, those skills weren’t necessary for the work available in Little Compton.
It requires a level of abstraction to see Stephanie and Corey as “being cheated,” because if the school committee were to offer the job for substantially more — the union’s doubled rate, for example — then it would be much less likely that the young adults would have gotten the job in the first place. As is often the case, the folks at the bottom compose one group that is harmed by the urge to dictate terms to the free market, because such dictation extends its benefits up the payscale. The person who would be more qualified to take a simple painting job at $14 per hour would not have to take work more suited to his abilities, and so on up the line, ultimately costing society productivity and resources that it ought to have achieved.
That chain leads to the other group harmed by the rejection of the free market — the consumer — and to BAM’s subsequent thought:

As to who “owns” the job, that’s a legal question that neither you nor I have enough knowledge to address. I’m not a lawyer, and neither are you.

I’m not sure why one would need a law degree to address questions of job ownership. Even if painting were in the union’s contract, it could scarcely claim ownership. Could the union declare that the work does not exist and will not be done? Could it create new similar work on its own authority? Creation and nullification are the markers of ownership and rest entirely with the school, in this case.
If it is not so, then the public consumers — the taxpayers — have all the more reason to ensure that the self-interested unions, claiming to be owners of their own patronage at others’ expense, are extricated from the equation.