This is both unethical and illegal. Interestingly enough it's under the enabling statutes for labor unions and collective bargaining (Clayton Act) that unions are exempted from antitrust legislation.
"The labor of a human being is not a commodity or article of commerce."
Clayton Act, sec. 6, c. 323, 38 Stat. 730 (1914)
See also 15 USC 17 ...
TITLE 15
§ 17. Antitrust laws not applicable to labor organizations
The labor of a human being is not a commodity or article of commerce. Nothing contained in the antitrust laws shall be construed to forbid the existence and operation of labor, agricultural, or horticultural organizations, instituted for the purposes of mutual help, and not having capital stock or conducted for profit, or to forbid or restrain individual members of such organizations from lawfully carrying out the legitimate objects thereof; nor shall such organizations, or the members thereof, be held or construed to be illegal combinations or conspiracies in restraint of trade, under the antitrust laws.
It must be understood that "supply and demand" and "labor market" are terms and concepts that treat human labor as a commodity. This, in a tahitinutshell, is corruption. When we see truckloads of laborers being
smuggled across the border like so many cattle, that's treating labor as a commodity. Slavery is the commoditization of human labor.
It is a fundamental evil. It corrupts all who participate.