Go back further. Minimums were applied to the railroad in 1909, pulling them up to the prevailing white wage when the Brotherhood of Locomotive Firemen became enraged blacks were working for cheaper.
I don't see anything about a minimum wage. I do see 'the arbitrators did rule that the railroad would be required to pay African American and white firemen the same wage' but nothing about how that minimum was set by law.
Minimums for a union job are not the same as minimum wage, which is the legal minimum set by law.
Union minimums predate the Civil War. For example, the Boston Journeymen Bootmaker's Society had a minimum price per shoe made, back in the 1830s, leading to Commonwealth v. Hunt.
