Oregon Revised Statutes Elections § 253.700

(1) The county clerk, an elections official or any elector shall challenge the ballot of any person offering to vote as an absent elector whom the clerk, official or elector knows or suspects not to be qualified as an elector. The person's ballot may be challenged at any time before the ballot is removed from its return envelope for processing.

(2) A challenge to a ballot of a person offering to vote shall be made under oath or affirmation before the clerk and shall be in writing on a numbered challenge form. 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. Any elections official may administer the oath or affirmation required under this subsection.