Norm Matloff of UC Davis has literally been trying to expose this for decades, with little luck:
http://www.cs.ucdavis.edu/~matloff/h1b.html
http://www.cs.ucdavis.edu/~matloff/h1b10min.html
Moreover: this is entirely consistent with behavior of employer first observed in the 18th century:
[I]n every part of Europe twenty workmen serve under a master for one that is independent, and the wages of labour are everywhere understood to be, what they usually are, when the labourer is one person, and the owner of the stock which employs him another.
What are the common wages of labour, depends everywhere upon the contract usually made between those two parties, whose interests are by no means the same. The workmen desire to get as much, the masters to give as little, as possible. The former are disposed to combine in order to raise, the latter in order to lower, the wages of labour.
It is not, however, difficult to foresee which of the two parties must, upon all ordinary occasions, have the advantage in the dispute, and force the other into a compliance with their terms. The masters, being fewer in number, can combine much more easily: and the law, besides, authorises, or at least does not prohibit, their combinations, while it prohibits those of the workmen. We have no acts of parliament against combining to lower the price of work, but many against combining to raise it. In all such disputes, the masters can hold out much longer. A landlord, a farmer, a master manufacturer, or merchant, though they did not employ a single workman, could generally live a year or two upon the stocks, which they have already acquired. Many workmen could not subsist a week, few could subsist a month, and scarce any a year, without employment. In the long run, the workman may be as necessary to his master as his master is to him; but the necessity is not so immediate.
Marx, you ask? No. Engles? No.
That's Adam Smith, Wealth of Nations
http://www.gutenberg.org/files/3300/3300-h/3300-h.htm#link2H...