Sinanju said:
I'm not sure of the canon, but IMTU the Imperium controls space; member worlds can run their own affairs as they see fit. So while slavery on a particular world can be legal, the "employment" or transport of slaves thru Imperial space would be illegal. A lot of worlds do a lot of things that the Imperium dislikes, but so long as they abide by the few rules the Imperium enforces (no nukes, no interstellar warefare, no slave trafficking between worlds), it doesn't get involved.
. . .
I would argue that the ban on slavery supersedes local law. But because the Imperium has a lot to do just maintaining its borders, business interests, etc., and only so many resources to enforce supposedly absolute laws, enforcement is spotty.
If slavery is extensive and obvious, a government can expect to face naval interdiction. A couple of frigates are all it takes to shut off outside trade, so that's easy for the Imperium unless there's a substantial naval conflict in the vicinity. If the economic pressure of interdiction doesn't force the government to give up slavery, there's a fair chance that regime change will happen -- through funding of anti-slavery locals, assassins, or a military strike -- as soon as someone decides to take action. Maybe the interdiction costs too much in lost trade on the other side, maybe there's a military unit that needs training in live combat, or maybe someone in power just abhors slavery.
On the other hand, if slavery is on a small scale (a minor nation on a balkanized would that's already ostracized by other nations, for example), or covered by sufficient legal fictions (abusive indentured servitude, prison labor, company towns, etc.), Imperial powers may let it slide. But if a new noble inherits oversight of the world, and strongly opposes slavery, the planetary or national government might face an ultimatum, and possibly regime change.