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.
ORS 663.135