Duty levied on imports from foreign polities.
Different polities and empires have different rules regarding customs, tariffs, and other political-border considerations. Much of this is handled at the stargates, usually as a transit fee for ships not staying. Stargates are easy to control, so this is where the big political control mechanisms can work. For ships and cargo that are staying, local rules come into effect. They can range from nearly nothing ("Welcome to Vast Enterprise, your gateway to the greater NoCoZo. Please note that this is a Tier III society, and adjudication insurance and/or a protection company is a good investment. This message was brought to you by Welcome Corporation. Have a profitable stay!") to nanoprobes through every orifice of the ship, passengers and cargo ("This ship will be fined 0.450 H-credits for the nonstandard color scheme").