For example, the Liberty Navy can shoot Xenos in Kepler, because the Xenos are hostile and in the LN zone of influence. This hostility is determined by story-controlled NPC faction diplomacy and does not rely on player roleplay laws.
What the LN ship can't do is confiscate cardamine from a Freelancer in Cortez. This is a different matter, and "ships hostile to" is not only defined by "can enforce laws".