A couple of paranoid gun nuts in Avon, Colorado are suing for the right to bring guns into the post office. Leaving the guns on a car parked on the across the street is just too much of an infringement on their right to bear arms, they think. Never mind that their choice makes everyone else less safe.
The rule they seek wouldn't necessarily have wide application, however. Avon is unusual in not having home mail delivery (FWIW, a better idea than cutting Saturday mail delivery that would build community and make sense in far more places).
Their battle makes fighting for the right to party and bra burning look positively respectable and non-violent by comparison.