Colorado did a state amendment by referendum to actually ban slavery, but when a prisoner went to court to stop his slavery, the judge said the people obviously did not mean to ban slavery when they voted to ban slavery.

"the voters did not intend to abolish the DOC inmate work program by virtue of passing Amendment A," wrote Judge Sueanna P. Johnson

The text of Amendment A which the voters voted on was:

"Shall there be an amendment to the Colorado constitution that prohibits slavery and involuntary servitude as punishment for a crime and thereby prohibits slavery and involuntary servitude in all circumstances?"

Frederick Douglass, arguing for unity among black and white laborers in 1883, said that “experience teaches us that there may be a slavery of wages only a little less galling and crushing in its effects than chattel slavery, and that this slavery of wages must go down with the other.”

The critique of wage slavery was then taken up by anarchists, socialists, and labor radicals of various stripes, who railed against the capitalist labor market and organized for a multiracial struggle against the owners of capital. Lucy Parsons, born a slave and later a widely known anarchist, declared in one of her most famous speeches:

How many of the wage class, as a class, are there who can avoid obeying the commands of the master (employing) class, as a class? Not many, are there? Then are you not slaves to the money power as much as were the black slaves to the Southern slaveholders? Then we ask you again: What are you going to do about it? You had the ballot then. Could you have voted away black slavery? You know you could not because the slaveholders would not hear of such a thing for the same reason you can’t vote yourselves out of wage-slavery.

from https://www.jacobinmag.com/2020/01/wage-slavery-bernie-sanders-labor

https://www.youtube.com/watch?v=BP2rm9zLAJQ