At War

Argent Dawn faction panel with "At War" checked

The At War checkbox in the Reputation panel allows a character to attack members of a faction that are not usually hostile toward them. If checked, the character can initiate combat and deal damage to NPCs of that faction.

Members of the opposing factions are always at the lowest reputation level of hated and are permanently set to the At War state. This option cannot be enabled for other races within a character's own faction.

Bugs

In 4.0.x, if your reputation with a faction is friendly or higher, you cannot attack members of that faction with melee attacks, ranged attacks, or any spells that require an enemy target—even if you've checked the "At War" checkbox for that faction.

The only way to attack such NPCs is to use AoE attacks on them.