Slave labor is also a colloquialism for poorly paid work. The Cambridge dictionary for example says it has an “informal disapproving” sense of “very hard work f

Slave labor is also a colloquialism for poorly paid work. The Cambridge dictionary for example says it has an “informal disapproving” sense of “very hard work for which people are paid very little” and has an example sentence of “It’s slave labor working in that office”. Dictionary.com’s example is “data entry at that salary is slave labor.” You can argue that colloquialism is a crass juxtaposition of horrifying slavery and things far less horrifying, but it’s clear to me the OP was using it in that informal sense, and is probably quite aware slavery was a terrible thing.