… is from page 129 of my great colleague Walter Williams’s 2010 autobiography, Up From the Projects  (footnotes deleted; link added):
In April 1981, I was asked to give testimony before the Senate Labor Committee on the Davis-Bacon Act [of 1931] . During Ray Marshall’s term as secretary of Labor in the Carter administration, he had testified before the corresponding House sub-committee that Davis-Bacon did not have discriminatory effects on non-union workers and blacks. The fact, however, is that the act was racially motivated law, and it sought to prevent black construction workers from competing with their white counterparts.
Consider the following examples of the 1931 testimony in support of the legislation: Representative Clayton Allgood of Alabama said, “Reference has been made to a contractor from Alabama who went to New York with bootleg labor. This is a fact. That contractor has cheap colored labor that he transports, and he puts them in cabins, and it is labor of that sort that is in competition with white labor throughout the country. This bill has merit, and with the extensive building program now being entered into, it is very important that we enact this measure.” Representative John J. Cochran of Missouri echoed similar sentiments, saying that he had “received numerous complaints in recent months that Southern contractors employing low-paid colored mechanics getting work and bringing the employees from the South.” William Green, president of the AFL, made the union position’s clear: [C]olored labor is being sought to demoralize wage rates.”
Ignorant, bigoted, and benighted politicians and labor-union officials – bent on nothing more noble than creating special privileges for the politically influential at the expense of the politically most vulnerable – have no trouble understanding the basic economic insight that raising the cost to employers of using certain kinds of labor increases employers’ incentives to substitute out of that kind of labor and into some alternative methods of production. In stark and sad contrast, today’s “Progressive” politicians, pundits, professors, and preachers seem unable to grasp this simple point.