"The earliest of such laws were regulations passed in regards to the railroad industry. At the end of the nineteenth century, as Dr. Walter Williams points out, "On some railroads — most notably in the South — blacks were 85–90 percent of the firemen, 27 percent of the brakemen, and 12 percent of the switchmen."
The Brotherhood of Locomotive Firemen, unable to block railroad companies from hiring the non-unionized black workers, called for regulations preventing the employment of blacks. In 1909, a compromise was offered: a minimum wage, which was to be imposed equally on all races....
But this new wage rule, of course, did not eliminate the racism of nineteenth-century employers. Instead, it displaced their racism at the expense of black workers. One white union member at the time celebrated the new rule for removing "the incentive for employing the Negro." This early minimum wage rule was explicitly put in place to prevent African-Americans from finding employment, and it was successful in this goal."
https://mises.org/blog/racist-history-minimum-wage-laws
The Brotherhood of Locomotive Firemen, unable to block railroad companies from hiring the non-unionized black workers, called for regulations preventing the employment of blacks. In 1909, a compromise was offered: a minimum wage, which was to be imposed equally on all races....
But this new wage rule, of course, did not eliminate the racism of nineteenth-century employers. Instead, it displaced their racism at the expense of black workers. One white union member at the time celebrated the new rule for removing "the incentive for employing the Negro." This early minimum wage rule was explicitly put in place to prevent African-Americans from finding employment, and it was successful in this goal."
https://mises.org/blog/racist-history-minimum-wage-laws