Literally the first ddg result for occupational licensing racism: https://www.minneapolisfed.org/article/2022/how-occupational...

EDIT: oh I guess I read too hastily and this is about the original motivation. For that you'd probably want to read Competition and Coercion by Robert Higgs. A lot of statutes and ordinances were adopted in the wake of the South's loss in the Civil War to maintain the status quo of white dominance in business