Here is the full context which still permits slavery so long as you've done a crime(and what counts as a crime can be modified to get the exact amount of slave labor you need)

Section 1. Neither slavery nor involuntary servitude, except as a 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 2. Congress shall have power to enforce this article by appropriate legislation.