It's pretty wide question, which, for sure, contains innumerable sub-questions.
For example, is it legal for planetary government to enslave distinguishable part of planet's population (not criminals!) and then resell to the world's financial elite with the aim of making better economy using obtained money?
Can it be legal for owner in some planetary jurisdictions to kill privately held slave with no other reason than just because he finds murder joyful?
Etc., etc., etc...
What is the exact situation with slavery in the Imperium of Mankind? Which forms of slavery CAN be legal at least in the some parts of Empire? And are there any forms of slavery which CAN NOT be legal anywhere in the Empire?
So, the status of slavery, very broad question.
Thanks. A lot! And sorry for my English, please.