8.2.2 - Shooting into Melee Combat

A unit that is within 3" of any enemy units can only target enemy units that are within 3" of it. Vehicles and Aircraft type units may only target a unit within 3" with Secondary Weapons they are equipped with.

You may not target enemy units that are within 3" of another friendly unit unless the attacking unit is also within 3" of the target unit.

Units fire Snap Shots (8.2.1) with their shooting attacks unless they are attacking with Pistol Type weapons (see 8.4.1) when shooting into a unit within 3".