Oregon Revised Statutes Revenue and Taxation § 319.835

The Department of Transportation may investigate refund applications and gather and compile such information in regard to the applications as it considers necessary to safeguard the state and prevent fraudulent practices in connection with tax refunds and tax evasions. The department may, in order to establish the validity of any application, examine the books and records of the applicant for such purposes. Failure of the applicant to accede to the demand for such examination constitutes a waiver of all rights to a refund on account of the transaction questioned.