Home Rule Authority
Oregon is a "home rule" state which means cities have broad authority under state and federal law to govern within their jurisdiction. That power is derived from the city charter. If a city ordinance or action is called into question, there is a two step test to determine the validity of that action. First, that action must be authorized by the city charter. Second, that action must be compatible with state and federal law.
Essentially, cities have authority to act in whatever way they see fit for their jurisdiction unless that power has specifically been preempted by the Legislature. Refer to the White Paper on Home Rule for further information.