The Pier is part of the port system at Astoria. It is a port of call for cruise ships. The port does receive significant funding from transients but I think the area outside the port (the city that controls the port) does not have significant infrastructure and so the port funds a great deal of the local economy. They don't want to increase the cost of calling on the port for cruise ships and destroy that economy. They look outwards for ways to find other monies to support the port and they see these ships going by...There is a little more to it.
The Pier 1 is reserved for emergency repair of ships found unsafe by coast guard inspection. When this happens, there are docking and repair fees paid to the port during the time the pier is in service. Seems the problem is that it is not in continuous use. The idea is that since it is set aside for the convenience of commercial shipping in case they need emergency (or even maintenance) prescribed by the safety inspection prior to going to sea, the convenience of that pier could be charged to virtually all commercial shipping transiting the area.
A good point made by maritime law experts is that it may not fly due to previous attempts to invoke similar fees at other locations being shot down by the federal government as it involves international maritime law of transit. If Astoria is successful invoking a fee for all passing ships, this fee will be taken into consideration along with all other costs of doing business in all areas serviced by the waters surrounding the port.
Additionally, if they are successful, other ports may do the same. I think the affect on maritime law will be the most talked about aspect if the port is successful in implementing a transit fee in any form.
Finally, if they are successful in implementation, they have the problem of prior notification. They will be required to notify all transiting ship services of their intention to implement prior to implementation. Depending upon the vehicle they use to publish the information, publication itself may be cost-prohibitive, depending upon of course their fee structure.