Technoserfdom. Neofudalism under the traditional institutions. Slavery is something else quite terrible and not an image that one wishes to conjure. But yeah, bad idea for freedoms.
The lowliest slave could hope to escape to the North and be free, if we talk about US style slavery.
Or have their owner grant them freedom if we talk ancient Greece, Rome, etc...here not only the owner BUT the state has to agree as well.