Oregon Revised Statutes Revenue and Taxation § 323.607

If the Department of Revenue finds that an amount of gross purchases net of discounts equal to 25 percent or more of the gross purchases net of discounts as reported on the taxpayer's tobacco products tax return has been omitted from the return, the department may give notice of deficiency as prescribed in ORS 305.265 at any time within five years after the date the return was due or filed, whichever is later.