Milord
In addition to all the charges Sasha brings up, your other big hammer, (because it is called a "slave" contract) depending on exactly what types of activities this slave is required to perform, it could run afoul of the 13th Amendment.
"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."
Now I don't know of any cases linking this to a D/s arrangement. But it would make for an interesting hearing. The closest I am aware of it being invoked was for cases of conservatorship where conservatees wanted out.
I have heard of a situation where an 18 year old in Kansas did sign a slave contract, abuse happened, and the abuser took a plea for 20 years for a federal charge of "enticing a minor into illegal sexual conduct." There were conspiracy and sex trafficking charges against additional defendants, including his wife. My memory is hazy, but I believe chastity piercings may have been involved.