Oregon Constitution Art. IX § 9

Benefits payable under the federal old age and survivors insurance program or benefits under section 3(a), 4(a) or 4(f) of the federal Railroad Retirement Act of 1974,  1 as amended, or their successors, shall not be considered income for the purposes of any tax levied by the state or by a local government in this state. Such benefits shall not be used in computing the tax liability of any person under any such tax. Nothing in this section is intended to affect any benefits to which the beneficiary would otherwise be entitled. This section applies to tax periods beginning on or after January 1, 1986.