As you may know, historic Christianity has long considered the "Four Sins That Cry Out to Heaven" to be--- based on Scripture ---
It seems to me that this "defrauding workers" is not just a sin of a rapacious employer, but also of a coercive government agency, Union, or other entity which uses force or the threat of force to steal the honest wages of a working person.
In other words, excessive taxation, confiscatory fines for dicey reasons (e.g. dubious eEPA violations) and coerced payments for stuff like Union dues or Obamacare--- are all examples of "defrauding workers of their just wages." They are injustices that cry out to Heaven for vengeance.
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The Bible describes various forms of greed, one of which is rapaciousness. There is greed that involves wanting stuff without working for it. Simple laziness (sloth). But, this is mostly a self-victim crime. For this to work, you’d need an enabler. The State can be an enabler. And this would be wrong.
Then there’s a more pro-active form of greed, which is rapaciousness. This leads to lying, cheating, and stealing. You give the example of paying workers less than the agreed-upon wage. This is an other-victim crime and is a proper concern of the state. The Pope seems to think this is controversial. As though there are some people who are o.k. with dog-eat-dog style capitalism. I don’t know any capitalist who describes dog-eat-dog capitalism to be capitalism. We call that anarchy. It is a bogeyman concept employed by critics of capitalism.
Especially, the state is to protect the vulnerable among us from the liars, cheats, frauds, thieves and other criminals. I’m not sure “the vulnerable” should be synonymous with “the poor.” By “the vulnerable,” I mean children, those enfeebled by old age or disability, those of limited intelligence, of poor habits, and having other human frailties.
Perhaps most people can take care of themselves in the rough and tumble of the marketplace, but I don’t think anybody thinks everybody can. There are roles, then, for the State, the family, and for the church and other fraternal and charitable associations in a free society. In contrast, with socialism, we are atomized, and without need of family, church or other forms of free association.