Sorry, it was outlawed along with the other forms of slavery by the Thirteenth Amendment.
The Thirteenth Amendment hardly outlawed slavery or involuntary servitude. It just made them government monopolies.
Amendment XII:
Section I: Neither slavery nor involuntary servitude, except as punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Section II: Congress shall have the power to enforce this article by appreopriate legislation.
Note that slavery, *as punishment for crime whereof the party shall have been duly convicted*, remains legal in the United States...if the government does it.
-archy-/-
Indentured servitude isn't punishment for a crime.
Read a book.