The Department of Revenue may not apply an administrative rule in a manner that requires a change in the treatment of an item of income or expense, a deduction, exclusion, credit or other particular on a report or return filed by a taxpayer if:\n(1) The taxpayer filed the report or return by the date it was due; and\n(2) The treatment of the item on the report or return was consistent with an administrative rule adopted and in effect at the time that the report or return was filed. [2009 c.494 §2]
Oregon Legal Code