ARC (Animal Rights Consortium)
While not part of the Syndicate, ARC serves their interests in a limited capacity.
The Animal Rights Consortium (or ARC) is a coalition of groups such as Biopeace, Xenolifer, and the ISPCA (InterStellar Project Caring for Animals) that formed sometime in the mid-25th century. ARC claims to speak for the creatures that can't speak for themselves, which usually translates to the non-sentient (although they have intervened in sectors where specism is particularly rampant, like Terra Gamma). In a sense they're like a modern-day equivalent of the long defunct PeTA (People for the ethical Treatment of Animals) back on Earth, but genuinely support their alleged cause - euthanasia isn't seen as some sort of liberation for animals but rather punishment for those who allow harm to befall innocent creatures.
Although their arguments aren't much different from those made at the dawn of the millenium, public reception towards them have shifted. Advancements in "artificial" meats have made more people opposed to traditional "murdermeat" when alternatives exist (although a minority of ARC members believe plant-based and synthetic meats are just as bad). However, very few alien lifeforms seen so far are what humans would describe as "cute", which makes demanding their protection more difficult (to say nothing of xenomorphs). While words are sometimes enough to get their way, the group isn't above resorting to violence.
ARC isn't actually part of the Syndicate - too many members of the coalition are just as if not more guilty of animal abuse than Nanotrasen. However, they're more than willing to take jobs targetting the megacorporation from Syndicate members they don't have a beef with (no pun intended). It just so happens plenty of them see the merit in disrupting NT's mining operations and animal testing, even if they lack experience (or market share) in those fields.