It's only partially about work conditions
Some people assume it's only about work conditions, but this is not about what one would usually call "work conditions" (hours, pay, rest room breaks, stuff like that).
The issue that is irritating workers is that Apple has raised quality standards (to avoid the scratches that many of the iPhone5 in the first batch had out of the box), actually blemishes smaller 0.001 inch will not be accepted any more. Which would be well enough, if the workers would be thought how to do it, but they lack even the instruments to detect these blemishes themselves.
Basically, because of poor material selection considering durability, so that they have a phone that feels "good" and "expensive", Apple has chosen materials known to scratch easy. Now that some reviewers started to complain, they solved it by turning on the heat on the work force. As some people have pointed out, this kind of blemishes are in fact not fixable with exalate aluminium.