Bladerunner replicants are slaves, and look what happens to them if they decide they don't want to be slaves anymore.
This applies to worlds in Traveller since the technology exists to create biological machines - androids/replicants, call them what you will. I've used replicants on many a TL9-11 world IMTU.
Then there are the tank grown in-vitro fertilised second class citizens as presented in Space: Above and Beyond (ignore the war with the chiggs and concentrate on the struggle between humans, tanks and machines and you have quite an interesting setting).
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There are many interesting ways to get slavery of some sort into Traveller.
I had a group once play in a campaign which began with them taken by slavers (influenced by Enemy Mine) and forced to work on hostile worlds.
I use all of the above in some form or another IMTU. Along with penal slavery for capital crimes inside the Terran Empire. Still, it isn't something that comes up in adventures very often except as stage dressing and background.
Gene Wolfe wrote a story back in the day called
The HORARs Of War that has replicant-type vat-grown soldiers that were developed for fighting a particularly nasty war against aliens. Wolfe explained that the story was very much about his own 'Nam experience, and it fairly reeks of that when you read it. The idea of the HORAR stuck with me since I first wrote my campaign so I advanced the idea to include condemned prisoners being altered to fight as HORARs, too, along with some of the alterations being available to ordinary humans wanting to amp up their attributes.
One of my earliest adventures involved one of those condemned prisoners that had been rebuilt as a HORAR deserting and wanting the players to help him get to a world where the alterations could be modified so he could pass for human before the Marine chasers could catch up with him. This was before Blade Runner so when that came out I added in the civilian android types and the appropriate police hunters who keep them from running away from wherever they are 'assigned'. All of this HORAR and replicant stuff is kept outside the Terran Empire, since only penal slavery is legal within it. HORAR alteration and service as a sentence for those crimes is a touchy matter and is not widely known by the public as something that happens - t is more of an urban legend to the average joe.
As for the civilian replicants (or android as I have called them), whether or not they are legally considered slaves depends on two things IMTU: A) if they are not within the jurisdiction of the Empire then the Empire doesn't care so long as whatever is going on doesn't constitute a threat to the Empire's security or trade, and B) whether or not the android can be considered intelligent and self-aware. The simple Turing test is not enough - the android has to be capable of creative expression unique to itself.
I had some rules from somewhere that I think may have come from an ancient issue of Space Gamer or something that allowed me to custom build all sorts of androids from various components and programs. Or maybe I dreamt it since I can't find any traces of it in my myriad boxes of stuff, but I did find two android models I wrote up decades ago, along with about a dozen or so pages of and written rules for creating custom built vet-grown androids, along with the alterations available for use with regular people.
They are surprisingly comprehensive and good - which is why I think they were from somewhere else and these are my expanded and modded versions. If anyone wants to look them over I'll scan the pages and send them off.
The two examples I have are of animals grown to assist scouts and Marines in recon units. The first is grown from a regular house cat matrix (Scoutcat) and the second from a leopard (Neopard). Sometimes I'm really surprised at how stodgy my imagination has become over the years when I find stuff like this hidden away in my reams of loose notes from yesteryear.
In fact, I think I'll go post these two in the Ship's Locker with some expanded notes to make better sense of them.