Oregon Revised Statutes Evidence and Witnesses § 44.090

(1) Every person who has been, in good faith, served with a subpoena to attend as a witness before a court, judge, commissioner, referee or other officer, is exonerated from arrest, in a civil case, while going to the place of attendance, necessarily remaining there and returning. The arrest of a witness contrary to this section is void, and when willfully made is a contempt of the court; and the officer making the arrest is responsible to the witness for double the amount of the damages which may be assessed against the officer, and is also liable in an action by the party serving the witness with the subpoena, for the damages sustained by that party in consequence of the arrest.

(2) But the officer is not liable in any way, unless the person claiming the exemption makes, if required, an affidavit stating:

(3) The affidavit may be taken by the officer and exonerates the officer from liability for not making the arrest, or for discharging the witness when arrested.

(4) The court, judge or officer before whom the attendance of the witness is required may discharge the witness from an arrest made in violation of this section.