Oregon Revised Statutes Labor and Employment; Unlawful Discrimination § 663.135

It is an unfair labor practice for a labor organization or its agents to require of employees covered by an agreement authorized under ORS 663.125 the payment, as a condition precedent to becoming a member of the organization, of a fee in an amount which the Employment Relations Board finds excessive or discriminatory under all the circumstances. In making such a finding the board shall consider, among other relevant factors, the practices and customs of labor organizations in the particular industry, and the wages currently paid to the employees affected.