Shooting through Friendly Units

[Zamik]

I wanted to know if there was any rule against shooting through friendly units, by which I mean one friendly unit shoots at an enemy unit with another friendly unit between. I was looking at the core rules, and I couldn't find anything about it. I was thinking about keeping a shooting unit behind another unit to activate Unleash hell when that front unit is charged, but my game group friends weren't sure about that. So is it legal to shoot through friendly units or do they block LOS or is there some other prohibition?

[KrispyXIV]

So long as your models can see the target, and don't have another different enemy unit within 3" of them, they can absolutely shoot ANY target in range and LOS.  

As most units/models won't fully block LOS, most likely you can shoot through most friendly models at will with no limitations.