Oregon Constitution Art. IX § 15

The state, a city, county, district or other political subdivision or municipal corporation of this state shall not impose, by ordinance or other law, a tax, fee or other assessment upon the transfer of any interest in real property, or measured by the consideration paid or received upon the transfer of any interest in real property. This section does not apply to any tax, fee or other assessment in effect and operative on December 31, 2009.