Why is there disagreement about “free labor” if wage labor is normal?

This is a very good question.

An employer specifying the conditions of employment is normal in wage labor.

So we should not make the disagreement sound as though any employer authority itself contradicts free labor.

The historical dispute was more fundamental.

The question was:

What distinguishes genuinely free labor from a labor relationship that reproduces important features of slavery?

For example:

Former slaveholder's possible conception

“You are no longer my property. You can enter a labor contract with me and receive wages. Therefore, you are a free laborer.”

Formerly enslaved person's possible conception

“I am legally free, but I also want control over my labor, my family, my mobility, and the possibility of acquiring land and establishing an independent livelihood.”

The disagreement therefore concerns the scope and substance of free labor, not whether employers can have legitimate authority over workers.

And this is exactly why Perrone's discussion of Reconstruction-era contract disputes is useful: she identifies a fundamental disagreement over the meaning of the Thirteenth Amendment and the legal consequences of emancipation.

So I would not write:

“The former slaveholder wanted to impose conditions and the former slave rejected all employer conditions.”

That would be too crude.

Instead:

Former slaveholders and formerly enslaved people could differ over what conditions were compatible with genuinely free labor and what degree of control workers should possess over their labor and economic lives.