Oregon Revised Statutes Elections § 254.415

(1) The county clerk, an elections official or any elector shall challenge the ballot of any person offering to vote whom the clerk, official or elector knows or suspects not to be qualified as an elector.

(2) The clerk, official or elector challenging the ballot shall make, under oath or affirmation before a county clerk or other elections official, a written and numbered statement of challenge. The statement shall contain the name and residence address of the challenger, the name of the person challenged and a statement of the facts upon which the challenge is based.

(3) A person's ballot may be challenged at any time before the ballot is removed from its return envelope for processing.