A port entity may receive instructions from the public authorities to give particular treatment to certain national port-users (owners of either ships or cargo). This treatment may limit the port charges which can be applied and hence the level of the benefit that can be re-allocated. The government may also issue an order to the port authorities prohibiting the departure of specified ships. Without declarations of war, ports may sometimes be temporarily blockaded, either close at hand or in the sea lanes, in order to obstruct exit or entry, or in the pursuit of those suspected or identified as engaged in illegal or hostile activity. Quarantine may also close port operations down, and may be a political instrument.