Upvote:6
I do not know of any specific stories like that of Vedius Pollio and Augustus, but Euripedes seems to have shown concern for slaves. This is perhaps his most famous line on the subject:
'Alas! how cursed is slavery always in its nature, forced by the might of the stronger to endure unseemly treatment.' (Hercuba, 332–334)
Edit: Here are some references regarding the legal protections afforded to slaves, which seem to have been put in place to protect the status quo and not out of any compassion for fellow human beings:
In Plato's Euthyphro, one of Euthyphro's hired labourers had killed a slave and so Euthyphro's father 'bound him hand and foot, threw him into a ditch, and sent a man here to Athens to ask the religious adviser what he ought to do.' Euthyphro, 4c
The entry on slavery in The Oxford Classical Dictionary (4th edition), in particular the last paragraph